Symposium Organizers
Harry Radousky Lawrence Livermore National Laboratory/
University of California-Davis
James D. Holbery GridMobility LLC
Laura H. Lewis Northeastern University
Frank Schmidt EnOcean GmbH
Z1: Energy Harvesting Materials I
Session Chairs
Laura Lewis
Harry Radousky
Monday PM, November 30, 2009
Room 206 (Hynes)
10:00 AM - Z1.1
First Principles Approach to the Prediction of the Thermoelectric Figure of Merit.
Dmitri Volja 1 , Marco Fornari 2 , Boris Kozinsky 3 , Nicola Marzari 1
1 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Physics, Central Michigan University, Mount Pleasant, Michigan, United States, 3 Research and Technology Center, Robert Bosch LLC, Cambridge, Massachusetts, United States
Show AbstractTernary skutterudite systems are the focus of current research as promising systems for thermoelectric applications (TE), particularly for power generation from a heat source. The efficiency of a material is described by the dimensionless figure of merit ZT. Currently considerable efforts go in the attempt to find novel systems with high ZT values around room temperature.Computational screening of novel materials requires theevaluation of relevant transport quantities in reciprocal space, with careful treatment of integrands and very dense samplings in order to achieve accurated, converged results.In this work we use first-principles calculations and aninterpolation scheme based on maximally localizedWannier functions to interpolate both the energy bands and the operator matrix elements, with a greatly reducedcomputational expenses.This approach allows for further improvements on the evaluation of transport coefficients by allowing the implementation of energy-dependent relaxation times.Phonon thermal conductivity is also studied within density-functional perturbation theory (DFPT) to obtain harmonic and anharmonic terms.We applied this methodology to CoGe3/2S3/2, CoGe3/2Te3/2 and CoSn3/2Te3/2. Significant improvements in the Seebeck coefficientsare observed, when compared to binary CoSb3.
10:15 AM - Z1.2
Theoretical Assessment of Thermoelectric Performance of Deformed and Doped (La and Nb) SrTiO3.
Alper Kinaci 1 , Cem Sevik 2 , Tahir Cagin 2
1 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 2 Artie McFerrin Department of Chemical Engineering & Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractStrontium titanate (SrTiO3), a well known compound among semiconductor oxides, is reconsidered as a thermoelectric material recently. In its pure, undeformed-bulk state SrTiO3 is inadequate for thermoelectric applications however; doping, alloying and straining can enhance the thermoelectric performance of that material. In this context, this study focuses on the detailed investigation of strontium titanate for its electronic transport parameters that describe the dimensionless figure of merit (ZT). The computations are based on the first principles, LDA, LDA+U and GGA calculations and Boltzmann theory in constant relaxation time approximation. Among several modifications, uniaxial tension-compression and simple shear in sensible straining range alters electrical conductivity only very slightly at high doping levels. Additionally, it is observed that there is almost no change in Seebeck coefficient for the same amount of deformation. Furthermore, we considered La and Nb alloying in 2x2x2 and 3x3x3 supercells in the form of Sr8-xLaxTi8O24, Sr27-xLaxTi27O81, Sr27Ti8-xNbxO81 and Sr27Ti27-xNbxO81 (x = 1, 2), and we have obtained very good agreement for Seebeck coefficient with available experimental data. Finally, relaxation times for several doping levels have been obtained to calculate electronic thermal conductivity and ZT by fitting electrical conductivity over relaxation time with experimental electrical conductivity.
10:30 AM - **Z1.3
Controlled Nanostructures for High Efficiency Energy Conversion and Storage.
Jun Liu 1 , Zimin Nie 1 , Guozhong Cao 2 , Qifeng Zhang 2 , Xiaoyuan Zhou 2
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , University of Washington, Seattle, Washington, United States
Show AbstractRecently the role of nanostructured materials in addressing the challenges in energy and natural resources has attracted wide attention. This talk will discuss the synthesis and applications of well-controlled nanostructures for energy harvesting, conversion and storage. We will demonstrate the importance of both the nano- and macroscale architectures. One example is using nanowires for dye sensitized solar cells (DSSCs). One-dimensional semiconducting oxides have attracted wide attention for dye sensitized solar cells (DSSCs), but the overall performance is still limited as compared to TiO2 nanocrystalline DSSCs. We will discuss the synthesis and study of aggregated TiO2 nanotubes with controlled morphologies and crystalline structures for DSSC applications, and report an overall power conversion efficiency as high as 9.9% using conventional dyes and without any additional chemical treatment steps. Examples of well-controlled nanomaterials for energy storage will also be highlighted.
11:30 AM - Z1.4
Reduction in the Thermal Conductivity of Thermoelectric Titanium Oxide by Introduction of Planar Defects.
Shunta Harada 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 , Kyoto University, Kyoto Japan
Show AbstractThermoelectric materials have been attracting great interest due to their potential application, such as electric power generation by waste heat and cooling system. The efficiency of thermoelectric materials are evaluated by the dimensionless figure of merit ZT =α2T/ρλ where Z, α, ρ, λ and T correspond to the figure of merit, Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature, respectively. Thermal conductivity is the sum of electronic and lattice contribution. Since the electronic thermal conductivity is related to electrical resistivity through Wiedemann-Franz law, materials with low lattice thermal conductivity which is independent of other physical properties listed above, can possess high thermoelectric performance. Recently, lattice thermal conductivity reduction in superlattice structure has attracted great attention. In the present study, we focused on Magnéli phase TinO2n-1. Crystal structure of Magnéli phase TinO2n-1 (n=3,4,5...) is rutile based structure with dense planar defects called crystallographic shear plane. Excess titanium atoms at crystallographic shear planes are located at interstitial oxygen octahedral positions and a corundum like structure is locally formed. As a result, oxygen deficiency occurs and homologous series of Magnéli phase TinO2n-1 is formed by changing the spacing of the shear plane. Thermal phonons are expected to be scattered at crystallographic shear planes, which reduce the lattice thermal conductivity. In the present study we investigated thermoelectric properties, especially thermal conductivity, for a series of Magnéli phase TinO2n-1. The powder of titanium oxides is produced by the solid state reaction of titanium monoxide and titanium dioxide. Dense polycrystalline ceramics were prepared by conventional hot pressing in vacuum. The values of Seebeck coefficient for all titanium oxides are negative in sign (n-type conduction) and the absolute values of Seebeck coefficient decrease with increasing oxygen deficiency. The values of electrical resistivity also decrease with increasing oxygen deficiency, which indicates the carrier concentration increases. Lattice thermal conductivity for titanium oxides decreases with increasing oxygen deficiency by more than 60% at room temperature and 40% at 773K compared to rutile. This implies that dense planar defects in titanium oxides scatter thermal phonon and reduce the lattice thermal conductivity. For titanium oxides, the maximum ZT value of 0.13 is obtained at 773 K, which is comparable to those of other non-oriented polycrystalline oxide so far reported.
11:45 AM - Z1.5
Solid-state Synthesis of Magnesium-doped Copper Aluminum Oxides.
Chang Liu 1 , Donald Morelli 1
1 Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractThermoelectric materials with high figure of merit are strongly demanded for waste heat recovery applications. Recently, copper aluminum oxide (CuAlO2) attracted attention due to its low thermal conductivity, high-temperature stability and low production cost. CuAlO2 possesses rhombohedral (R3m) delafossite structure, which is constructed by alternate appearance of two-dimensional layers. This structure promotes strong phonon scattering and low thermal conductivity. As an oxide, CuAlO2 is also more stable than conventional alloys at elevated temperature. To improve electrical conductivity and Seebeck coefficient, magnesium is investigated as a dopant to substitute for Al cation. Sample fabrication involves two stages. Firstly, powder samples are prepared by solid-state reactions. Aluminum oxide, copper (II) oxide and magnesium oxide powders are mixed at a molar ratio of Al: Cu: Mg=1:1-x: x (x=0 - 0.1) for 12 hours and then dried at 80 °C overnight. Powder mixtures are fired in a flat alumina boat in a tube furnace at 1373 K for 24 hours with heating and cooling rate of 5 °C/min. Continuous argon flow is applied to the furnace during the entire reaction process. As the second step, a hot-press technique is adopted to achieve high density bulk samples. As-prepared powders are pressed under 27.6 MPa at 1050 °C in air for 3 hours and yield bulk samples with over 95% of theoretical density. As comparison, powders are also cold-die pressed and sintered at the same temperature to fabricate pressure-less counterparts, which can only reach 60% of theoretical density.X-ray diffraction confirmed delafossite structure as dominant phase in all products. As the doping level rises, peak intensity of second phases, such as CuAl2O4, increased. In hot-pressed sample, CuO phase emerged, indicating oxidization of samples at elevated temperature in air. Peak shift in diffraction patterns also revealed lattice constant changes, which reached the peak at 2% doping ratio and decreased after that. Besides lower porosity, SEM images showed larger grain size in hot-pressed samples than cold-pressed ones. Transport properties were examined in a high-vacuum chamber using four-probe method. Electrical conductivity, Seebeck coefficient and steady-state thermal conductivity were measured at intervals of 10K from 90K to 300K. Mg doped sample shows a dramatically increased electric conductivity relative to pure CuAlO2. The hot-pressed sample exhibits both higher thermal and electrical conductivity than pressure-less sintered counterparts. Further transport property characterization, including carrier concentration and mobility, is underway.
12:00 PM - Z1.6
Thermoelectric Performance of Quaternary Compounds: Cu2ZnSnX4, X=S, Se, Te.
Cem Sevik 1 , Tahir Cagin 1
1 Artie McFerrin Department of Chemical Engineering & Material Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractFollowing a recent experiment on In-doped Cu2ZnSnSe4 [Appl. Phys.Lett. {\bf 94}, 122103 (2009)] showing promise for wide band-gap quaternary system to be a good thermoelectric material, we have analyzed the relevant transport properties of this particular system as well as related materials Cu2ZnSnS4 and Cu2ZnSnTe4 to assess if they may perform equally well. Using first principles density functional theory along with Boltzmann transport equations, we have calculated the Seebeck coefficients, conductivity, and power factors of closely related polymorphs with space groups: I-4and I-42m and P-42m respectively for each compound. Our calculated Seebeck coefficients for different dropping levels of Cu2ZnSn1-xInxSe4 have excellent agreement with experimentally reported ones. Parallel results for transport properties of different polymorphs has been pointed out as one the source of low thermal conductivity of Cu2ZnSnSe4. Additionally, another source of low thermal conductivity, possible substitutional disorders, have been investigated by total energy calculations of several lower symmetry structures generated through shuffling elements and sites. Finally, similar materials, Cu2ZnSnS4 and Cu2ZnSnTe4, have been studied and parallel results for electronic structure and transport properties, indicating similar potential for thermoelectric applications, have been obtained.
12:15 PM - Z1.7
Thermoelectric Properties of La1-xSrxCuO3-δ Ceramics.
Julio E. Rodriguez 1 , Luis C. Moreno 2
1 Department of Physics, Universidad Nacional de Colombia, Bogota Colombia, 2 Department of Chemistry, Universidad Nacional de Colombia, Bogota Colombia
Show AbstractThermoelectric properties of La1-xSrxCuO3-δ samples prepared by sol-gel method were studied in the temperature range between 100 and 290 K. From Seebeck coefficient S(T) and electrical resistivity ρ(T) measurements the thermoelectric power factor PF was calculated. S(T) is positive over the studied temperature range suggesting a P-type conduction, its magnitude increases with the Sr level reaching maximum values close to 125 μV/K. The temperature dependence of ρ(T) changes from semiconducting-like to metallic as the strontium increases, but in all cases ρ(T) exhibit values less than 8mΩ-cm. The thermoelectric performance was evaluated through the PF parameter, which shows maximum values close to 35 μW/K2-cm. These values become these oxygen deficient ceramics promising thermoelectric material for low temperature applications.
12:30 PM - Z1.8
Thermoelectric Properties of Sputtered Bi-Sb-Te/Sb Multilayer Films with Electric Current Assisted Annealing.
Chih-Yu Chang 1 , Chien-Neng Liao 1
1 Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu Taiwan
Show AbstractBimuth telluride-based compound has been considered as a promising candidate for thin-film thermoelectric devices due to its superior thermoelectric figure-of-merit at room temperature regime. We noted that an electric current assisted annealing can effectively enhance the carrier mobility of sputtered Bi-Sb-Te thin films. However, a reduced carrier density associated with the electrical annealing suggested that the composition of Bi-Sb-Te thin films needs to be adjusted for optimized thermoelectric properties. In stead of changing the composition of sputter target, ultra-thin Sb inter-layers have been introduced in between the Bi-Sb-Te thin films followed by electrical annealing treatment to modulate the composition of the Bi-Sb-Te thin films. The Bi-Sb-Te and Sb layers were consecutively sputtered on a polyimide coated Si substrate at room temperature using a Bi0.5Sb1.5Te3 Te alloy target and a pure Sb target, respectively. The as-deposited thin films were subjected to an electric current stressing at a density of 5×10^3 A/cm^2 and at temperatures ranging from 150 to 300 °C under nitrogen atmosphere using a rapid thermal annealing system. The results show that the multilayered Bi-Sb-Te/Sb specimens have 40% higher carrier concentration and 35% lower electrical resistivity than those of the bare Bi-Sb-Te specimens. According to the Hall measurement results, the Sb addition indeed increases the carrier density and has no adverse effect on the carrier mobility enhancement of the electrically stressed Bi-Sb-Te thin films. The results suggest that we can modulate the composition and in turn thermoelectric properties of the Bi-Sb-Te thin film by simply adjusting the Sb interlayer thickness. The effect of electric current stressing treatment on the electrical and thermal transport properties of the Bi-Sb-Te/Sb multilayered structure will be discussed in this study.
12:45 PM - Z1.9
Nanostructured Bismuth Films for Thermoelectric Power Application.
David Toledo 1 , Ashutosh Tiwari 1
1 Materials Science and Engineering, university of utah, Salt Lake City, Utah, United States
Show AbstractHere we report the synthesis and characterization of nanostructured thin films of high purity Bismuth (Bi). These films were fabricated using a state-of-the-art pulsed laser deposition (PLD) system. During this process a high purity solid target of Bi was ablated inside a high vacuum stainless steel chamber by a KrF excimer laser. Bi plasma thus produced was made to condense on glass and Si (100) substrates. Temperature of the substrates was varied over the range 140 K-523 K to introduce morphological changes in the films. Films thus prepared were thoroughly characterized using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), thermoelectric power, electrical resistivity and Hall effect measurements. Analysis of XRD peak broadening showed that as the temperature of the substrate during the deposition increases the average size of the Bi nano-grains increases systematically. Average grain size for the films deposited at 140K was ~20 nm while it increased to ~50 nm for the films deposited at 473 K. These kind of morphological variations also were observed in the FESEM micrographs, along with accurate measurements of film thickness. Thermoelectric power, electrical resistivity, carrier concentration as well as the carrier mobility were found to depend very sensitively on the morphology of the films. The electrical resistivity was found to depend very sensitively on the size of the nano-grains in the thin film. Our results showed that by carefully controlling the morphology of the films, thermoelectric performance of Bi films can be optimized.
Z2: Energy Harvesting Devices
Session Chairs
Monday PM, November 30, 2009
Room 206 (Hynes)
2:30 PM - Z2.1
Transient Thermal Imaging of Si/SiGe Superlattice Microrefrigerators.
Helene Michel 1 , Remi Coppard 1 , Dustin Kendig 1 , James Christofferson 1 , Younes Ezzahri 1 , Ali Shakouri 1
1 Electrical Engineering, University of California Santa Cruz, Santa Cruz, California, United States
Show AbstractMost of the conventional thermal management techniques in integrated circuits can be used to cool the whole chip. Since thermal design requirements are mostly driven by the peak temperatures, reducing or eliminating hot spots could alleviate the requirement for the whole package, and so, is a key enabler for future generation IC chips. Microrefrigerators on a chip based on nanostructured thermoelectric materials have attracted lot of attention during the last 10 years. SiGe is a known bulk thermoelectric material for high-temperature power generation applications. Recently, Si/SiGe superlattice (SL) structures have been investigated for room temperature cooling. Si-based microrefrigerators are attractive for their potential monolithic integration with Si microelectronics. Here we present a systematic study of transient cooling performances in microrefrigerators based on different Si/SiGe superlattice structures and device geometries.The microrefrigerator is based on couple of microns thick Si/Si0.7Ge0.3 SL active layer, grown using molecular beam epitaxy (MBE). With the use of different SL thicknesses and device geometries, distinct cooling characteristics, such as the maximum cooling or fast response can be achieved. Three samples were analyzed. Sample A and B were fabricated on a Silicon substrate, and have a 3 and 6 μm Si/Si0.7Ge0.3 SL layer respectively. The superlattices are grown on a micron thick buffer layer due to the lattice mismatch with the substrate. Sample C has a 3 μm Si/Si0.7Ge0.3 SL directly grown on a thick SiGe bulk layer deposited on silicon substrate using chemical vapor deposition. In all three samples, a highly doped 0.5 μm Si0.9Ge0.1 cap layer was grown to get a good ohmic contact to the device. The SiGe micro coolers are fabricated with standard silicon integrated circuit technology. The cooler device areas were defined by etching mesas down to the buffer. Ti/Al/Ti/Au/ were made on top of mesa and on the buffer layer next to the mesa for top and bottom contact respectively. SiGe micro coolers with mesa sizes ranging from 30x30 μm2 to 150x150 μm2 were fabricated on the same wafer.Transient thermoreflectance thermal imaging is used to characterize the cooling of active semiconductor devices. One can obtain temperature maps with sub micrometer spatial, 100ns temporal and 0.1C temperature resolution. Transient thermal imaging of the microrefrigerators show that the Peltier cooling dominates in the first 10-30 microseconds before Joule heating in the active and buffer layers reach the top surface. Time characteristics of the Peltier cooling and Joule heating in the device are studied as a function of the superlattice thickness, device size and the buffer layer composition.
2:45 PM - Z2.2
Nanorectennas for Energy Harvesting.
Richard Osgood 1 , Joel Carlson 1 , Diane Steeves 1 , Caitlin Quigley 1 , Brian Kimball 1 , Gustavo Fernandes 2 , Jimmy (J.-M.) Xu 2
1 , US Army NSRDEC, Natick, Massachusetts, United States, 2 , Brown University, Providence, Rhode Island, United States
Show AbstractThere is renewed interest in using rectennas (consisting of an antenna coupled to a rectifying diode) for converting visible/near-infrared energy to direct current. Progress in nanofabrication has enabled fabrication of “nanoantennas”, which resonate at visible/near-infrared (vis/nir) wavelengths, and ultrafast “nanodiodes”, capable of rectifying vis/nir frequencies (above 10^14 Hz). A nanodiode-coupled nanoantenna is a “nanorectenna”, whose efficiency has been recently modeled [1]. We simulate the resonance wavelength of nanoantennas, such as horizontal, patterned gold nanostructures on silicon (resonance wavelength predicted to be ~ 1100 nm, in agreement with experiment) and vertical gold nanowires grown on silicon. We present experimental work on nanoantenna-coupled NiO diodes, including metal-insulator-metal diodes and nanospheres on thin NiO layers, and discuss how the findings influence our nanorectenna model.[1] “Nanoantenna-coupled MIM nanodiodes for efficient vis/nir energy conversion,” Osgood, III R.M., B.R. Kimball, and J. Carlson, (2007), Optical Modeling and Measurements for Solar Energy Systems, ed. Daryl R. Myers, 6652:665203
3:00 PM - **Z2.3
Power Management in Energy Harvesting Applications.
Peter Spies 1
1 Power Efficient Systems, Fraunhofer IIS, Nuremberg, Bavaria, Germany
Show AbstractThe power consumption of electronic circuits and systems is decreasing more and more. On the other hand, the efficiency of energy harvesting transducers like thermo-generators, piezoelectric modules or solar cells is being further optimized. Therefore, nowadays energy from the environment like heat, light or motion can be used to supply low-power electronic devices. To use minimum amounts of harvested energy as efficient as possible, special focus is on the power management in form of voltage converters, impedance matching and control circuits. All these circuit blocks have to be designed taking into account the limitations associated with energy harvesting transducers, which are low currents and low voltages. Each energy transducer principle like thermoelectric, piezo-electric or electro-dynamic requires its own tailored voltage converter. The approaches are much different because the nature of the generated voltage and current profile are quite conflictive. With proper electronic power management design the useable energy from the energy transducer could be increased significantly. Material design parameters especially the electrical impedance of the energy transducer are influencing the electronic circuit requirements and affect the energy output. Design trade-offs between material and electronics have to be considered. Improvements in power management can lower the requirements to the transducer itself and influence the size and cost parameters. This can have a significant impact on the possible application areas. Additional circuitry and their properties have to adapt the power management to the changing ambient conditions like variable thermal gradients, changing vibration frequencies or fluctuating illumination. These modules will further increase the potential power output and ensure the maximum efficiency. Furthermore, they will extend the possible fields of applications and increase the return-on-invert of the development and design.
3:30 PM - Z2.4
Using Plasmonic Scatterers in Ultrathin-film Solar Cells to Approach the Absorption Limit of Bulk Materials.
Jeremy Munday 1 , Vivian Ferry 1 , Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractUltrathin-film (tens to hundreds of nm) photovoltaics could allow high efficiency cells to be produced using significantly less material and hence at a lower cost. However, one of the main disadvantages of ultrathin-film photovoltaics is the difficulty in achieving high photocurrents when the cell thickness is significantly thinner than the absorption length of light within the material. To overcome this difficulty, we consider ultrathin-film, direct-bandgap GaAs cells with plasmonic scattering objects, which are capable of efficiently scattering light into the absorbing layer. Finite difference time domain (FDTD) simulations are used to determine the optimal structure for enhanced light absorption and carrier generation, which can be used in device modeling. For the case of a 200 nm thick GaAs film with a silicon nitride antireflection coating, we compare the absorption between two cells: one with an array of 50 by 150 nm silver back scatterer grooves and one without. The plasmonic back scatterers are found to increase the absorption by nearly 20% when weighted over the AM 1.5 spectrum. More surprisingly, we find that the 200 nm thick film with plasmonic scatterers can absorb more than 80% of the incident light that an optically thick GaAs cell with similar antireflective coating would absorb. Experimental results will also be discussed for ultrathin GaAs cells with plasmonic scatterers on the top surface of the cell. Because the ultrathin film cell requires an order of magnitude less material, such designs could dramatically reduce the amount of material needed for such cells and lead to the rapid development of high efficiency, ultrathin-film photovoltaic solar cells. Further, plasmonic scattering could be used in a variety of other light harvesting devices using the same principles applied to increase the absorption in solar cells.
3:45 PM - Z2.5
Angle Dependent Energy and Yield Distributions of Forward Scattered Electrons in a Supercapacitor Nanostructure used for Direct Nuclear to Electric Energy Conversion.
Claudiu Muntele 1 , Daniel Wilder 2 , Abdalla Elsamadicy 2 , Liviu Popa-Simil 3 , Daryush Ila 1
1 , Alabama A&M University, Normal, Alabama, United States, 2 , University of Alabama in Huntsville, Huntsville, Alabama, United States, 3 , LAVM Inc, Los Alamos, New Mexico, United States
Show AbstractMost of the exothermic nuclear reactions transfer the mass defect or binding and surplus energy into kinetic energy of the resulting particles. These particles are traveling through material lattices, interacting by ionization and nuclear collisions. Placing an assembly of conductive-insulating layers in the path of such radiation, the ionization energy is transformed into charge accumulation by polarization. The result is a super-capacitor charged by the moving particles and discharged electrically. The direct application of such a structure is in a direct energy conversion scheme in a fission reactor, from nuclear to electric energy, bypassing the steam generation in a conventional cycle. There is a tremendous advantage over the current heat flow based thermal stabilization system allowing a power density up to 1000 times higher. Here we present experimental measurements of angle dependent energy and yield distributions of forward scattered knock-off electrons in gold and aluminum nanolayers used in a supercapacitive energy conversion system. We used 5 MeV alpha particles and 5 MeV gold ions incident to a gold-silica-aluminum sandwich and measured the forward electron distribution, with direct impact in the conversion efficiency of the device.
4:30 PM - Z2.6
Gate-tunable Thermopower of Silicon Nanowires.
Hyuk Ju Ryu 1 , Deborah Paskiewicz 1 , Shelley Scott 1 , Max Lagally 1 , Mark Eriksson 1
1 , UW-Madison, Madison, Wisconsin, United States
Show AbstractThermoelectric nano/microscale devices have been attracting interest as a compact and reliable solution for hotspot cooling in microchips. Special interest in silicon as a thermoelectric material arises because of the potential for monolithic integration in microchips, as well as opportunities to make use of silicon nanofabrication and bandstructure engineering to optimize thermal resistance, electrical conductivity, Seebeck coefficient, or all three. We present measurements of ambipolar thermopower and charge transport in silicon nanowires. For hole transport, the measured Seebeck coefficient varies monotonically with charge density. For electron transport, the Seebeck coefficient is nonmonotonic as a function of charge density and temperature. We discuss the optimization of the power factor in these silicon nanowires. The thermoelectric power of silicon nanowires can also be modified by the incorporation of heterogeneity in the form of interfaces between silicon/silicon-germanium and silicon/silicide, and between different crystalline orientations of silicon. Measurements of thermopower and charge transport in such nanowire heterostructures will be presented. This work is supported by AFOSR, DOE, NSF, and NDSEG.
4:45 PM - Z2.7
Metal/Semiconductor Superlattices on Silicon Substrates for Solid-State Thermionic Energy Conversion Devices.
Jeremy Schroeder 1 , Polina Burmistrova 1 , Robert Wortman 1 , David Ewoldt 1 , Timothy Sands 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractThermionic carrier transport in metal/semiconductor superlattices is a promising energy conversion approach based on nanocomposite materials. Despite the poor thermoelectric properties of the individual metal and semiconductor layers, metal/semiconductor superlattices are expected to enhance the power factor (S2σ) through energy barrier filtering while suppressing thermal conductivity (k) via interface scattering of phonons. Transition metal nitride superlattices, in particular, are promising structures for power generation applications using high temperature (750K-1100K) waste heat. In order to optimize the power density of thin-film thermoelectric devices, the superlattice leg length will need to be in the range of 50-100 microns. To mitigate the effects of thermal and electrical parasitics in the final device, the superlattice must be sandwiched between high thermal and electrical conductivity materials. This latter requirement will often necessitate the removal of the growth substrate, thereby placing restrictions on potential substrates.(Hf,Zr,W)N/ScN superlattices of varying periods were deposited on 100-MgO, polycrystalline Cu foil, and 100-Si substrates by reactive DC magnetron sputtering. First, 300nm metal buffer layers (ZrN or HfN) were deposited to accommodate lattice mismatch between the substrate and the rocksalt nitride superlattices. Then, superlattices were sputtered from Zr, W, Hf, and Sc targets at 200W power in an Ar(4sccm)/N2(6sccm) ambient at 5mTorr with a substrate temperature of 850oC. The resulting film orientation, texture, and microstructure were characterized by high resolution x-ray diffraction (HRXRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). High quality epitaxial nitride superlattice structures based on (Hf,Zr)N/ScN where (Hf,Zr)N is the metal and ScN is the semiconductor barrier were grown on MgO substrates; however, MgO is not a scalable substrate solution, and is difficult to remove by selective etching. Copper is an ideal substrate from the standpoint of thermal end electrical conductivity, but the growth stress and thermal expansion mismatch between Cu and the nitride superlattices results in severe curvature of the copper substrate. Silicon was subsequently explored as a suitable substrate due to cost, scalability, and its ability to be selectively etched. Unlike the epitaxial films grown on MgO, superlattices on silicon showed uniaxial texture and TEM revealed a columnar grain structure with superlattices within the grains. The effect of this film structure on the cross-plane electronic transport is still being investigated. However, the silicon substrate was selectively etched in tetramethyl ammonium hydroxide (TMAH) and gold contacts were deposited on both sides of the superlattice, which demonstrates that silicon provides a route forward towards realizing thermoelectric devices based on nitride metal-semiconductor superlattices.
5:00 PM - Z2.8
Waferscale (≥4 inch) Si and Si1-xGex Wire Arrays for Solar Cell Applications.
Kwang-Tae Park 2 , Jin-Young Jung 1 , Han-Don Um 2 , Sang-Won Jee 1 , Hong-Seok Seo 2 , Kye Jin Jeon 1 , Syed Abdul Moiz 1 , Junh-Ho Lee 1 2
2 Bio-nano technology, Hanyang university, Ansan Korea (the Republic of), 1 Chemical engineering, Hanyang university, Ansan Korea (the Republic of)
Show AbstractSilicon wire-based solar cells are one of the attractive candidates for next-generation photovoltaic devices; however, Si has a relatively weak absorption in infrared region, alloying with Ge allows for the useful range of the solar spectrum spanning into a longer wavelength band due to a lower bandgap of Ge.Here, we report the vertical Si and Si1-xGex wires fabricated by metal-assisted electroless etching at ≥4 inch wafer scale. Shallow junctions could be formed using plasma immersion ion implantation (PIII) and spin on doping (SOD) for making a radial p-n junction of wire-based solar cells. Scanning electron microscope (SEM) image of the Si and Si1-xGex wire arrays revealed the periodic, uniform arrays of a vertical wire which were patterned using a 300-nm-thick oxide mask with a hole size of 2 μm and 4 μm pitches. The diameter and a length of these wires are ~2 and ~20 μm, respectively.To measure the current-voltage (I–V) characteristics, a ~200-nm-thick Al layer was thermally evaporated on a wafer backside. Top contacts were made to the front surface with Ga/In melt spots and an electrical probe tip. I–V curves under illumination were measured using a solar simulator. Electron holography and scanning capacitance microscopy (SCM) were adopted to obtain two-dimensional doping morphologies of a radial p-n junction. Significant reduction of reflectance and a strong light trapping behavior was observed in the Si1-xGex wire structures compared to Si wires, which enables the much efficient absorption of photon energies lower than the Si bandgap.
5:15 PM - Z2.9
Advanced High-Temperature Thermoelectric Couples for Waste Heat Recovery Power Generation.
Thierry Caillat 1 , Su Chi 1 , Billy Li 1 , Erik Brandon 1 , Chen-Kuo Huang 1 , Jong-Ah Paik 1 , Jean-Pierre Fleurial 1
1 , Jet Propulsion Laboratory/Caltech, Pasadena, California, United States
Show AbstractApproximately a third of the energy consumed by the U.S. manufacturing industry is released as thermal losses. Various technologies, including thermoelectrics, are being considered to convert the industrial waste energy to electrical energy. The quality of waste heat varies greatly depending on the specific industrial process. High-temperature are desirable for thermoelectric waste heat recovery to warrant conversion efficiencies that may make this technology a viable option. New high-temperature and efficient thermoelectric materials and devices are of interest for industrial waste heat recovery. The Jet Propulsion Laboratory (JPL) has been developing over the years advanced thermoelectric materials and devices for high-temperature operation, including for use in Radioisotope Thermoelectric Generators (RTGs). RTGs generate electrical power by converting the heat released from the nuclear decay of radioactive isotopes (typically plutonium-238) into electricity using a thermoelectric converter. RTGs have been successfully used to power a number of space missions including the Apollo lunar surface science packages, the Viking Mars landers, Pioneer 10 and 11, and the Voyager, Ulysses, Galileo, Cassini and New Horizons to Pluto outer planet spacecrafts. These generators have demonstrated their reliability over extended periods of time (tens of years) and are compact, rugged, radiation resistant, and produce no noise, vibration or torque during operation. These properties have made RTGs suitable for autonomous missions in the extreme environment of outer space and on the surface of Mars. This report will review recent progress at the Jet Propulsion Laboratory (JPL) in the development of high-temperature thermoelectric materials and devices for use into advanced RTGs or thermoelectric waste heat recovery. Thermoelectric materials under investigation include the Yb14MnSb11 Zintl phase and nanostructured bulk n- and p-type SiGe alloys.
5:30 PM - Z2.10
Seebeck Coefficient on Rubrene Single Crystal Field Effect Transistors with PDMS as Gate Insulator.
Wenhao Hu 1 , Chi Wah Leung 2 , Paddy Kwok Leung Chan 1
1 Mechanical Engineering, Hong Kong Polytechnic University, Hung Hom, Hong Kong China, 2 Applied Physics, Gong Kong Polytechnic University, Nagoya Japan
Show AbstractFor organic semiconductor devices, such as organic thin film transistors and organic single crystal transistors, carrier transport properties play the central role on the device performance. The carrier transport properties can be revealed via the study of Seebeck coefficient (S), which is related to the transport of the thermally excited charge carriers. Because of the facts that the electronic contribution to the Seebeck coefficient is determined by the band structure and energy-dependent scattering mechanisms, and that the Fermi energy can be modulated by altering the gate voltage in a field-effect transistor, studying the Seebeck coefficients of field-effect-modulated organic single crystal, which is free of grain boundaries and contains less charge traps, can be an effective way of investigating the carrier transport properties in organic semiconductors. In the current work, the Seebeck coefficients are measured on field effect transistors based on rubrene single crystals grown by vapor phase deposition. In order to reduce the fabrication-borne defect on the molecular bonding, interfacial trap states and charge injection barriers, Polydimethylsiloxane (PDMS), as an insulator with elastic nature and high surface energy, is used as the dielectric layer. The electronic contribution to S in rubrene single crystal is investigated by the combination of photoluminescence and gate-voltage-dependent Seebeck coefficient. At room temperature, the Seebeck coefficient increases from +83.3 μV/K to +412.3 μV/K when the gate voltage changes from -21V to +21V, and at zero gate voltage, it sees a 39% decrease when an incident fluorescent light is shed on the device.
5:45 PM - Z2.11
Thermoelectric Generators Made with Novel Lead Telluride Based Materials.
Chun-I Wu 1 , Steven Girard 2 , Joseph Sootsman 2 , Edward Timm 3 , Robert Schmidt 4 , Duck Young Chung 5 , Ilya Todorov 5 , Mercouri Kanatzidis 2 5 , Harold Schock 3 , Eldon Case 4 , Timothy Hogan 1 4
1 Electrical and Computer Engineering Department, Michigan State University, East Lansing, Michigan, United States, 2 Chemistry Department, Northwestern University, Evanston, Illinois, United States, 3 Mechanical Engineering Department, Michigan State University, East Lansing, Michigan, United States, 4 Chemical Engineering and Materials Science Department, Michigan State University, East Lansing, Michigan, United States, 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFor the material (Pb0.95Sn0.05Te)1-x(PbS)x nanostructuring from nucleation and growth and spinodal decomposition has been reported to enhance the thermoelectric figure of merit over bulk PbTe, producing ZT of 1.1 - 1.4 at 650 K for x = 0.08. Thermoelectric modules made from (Pb0.95Sn0.05Te)1-x(PbS)x materials with various hot-side metal interconnections have been fabricated and tested. Short circuit current measured on unicouples of Pb0.95Sn0.05Te – PbS 8% (n-type) legs and Ag(PbSn)mSbTe2+m (p-type, LASTT) legs over 10 (A) for a hot side temperature of 870K, and a cold side of 300K. This is approximately 80% of the ideal value for the leg dimensions used. Hot pressed (Pb0.95Sn0.05Te)1-x(PbS)x materials has also been investigated for module fabrication. Investigations of hot-pressed (Pb0.95Sn0.05Te)1-x(PbS)x samples including electrical properties and the latest advancements in the fabrication and characteristics of modules based on these materials will be presented.
Symposium Organizers
Harry Radousky Lawrence Livermore National Laboratory/
University of California-Davis
James D. Holbery GridMobility LLC
Laura H. Lewis Northeastern University
Frank Schmidt EnOcean GmbH
Z3: Energy Harvesting Materials II
Session Chairs
Tuesday AM, December 01, 2009
Room 206 (Hynes)
10:00 AM - **Z3.1
Anisotropic Phase Transformation of Poly (Vinylidene Difluoride).
Ke Wang 1 , Rodrigo Cooper 1 , Hyungoo Lee 1 , Hong Liang 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractThe poly (vinylidene difluoride) (PVDF) has been widely studied for energy harvesting of MEMS devices. As a semicrystalline polymer, the PVDF has five crystallographic forms, α, β, γ, δ and ε, only the latter four crystalline structures possess permanent dipole moment. We investigate effects of microstructures of the poly (vinylidene difluoride) (PVDF) on its piezoelectricity for energy harvesting. Using combined experimental techniques of an atomic force microscope and a Fourier Transform Infrared Spectroscope, observation of surface morphology and phase transformation in time was made possible. We found that an applied stress induced the phase transformation between amorphous, α, β, and γ phases. Specifically, the amorphous was transformed into the β phase. The transformation was time and direction dependent. Such transformation influences the energy harvesting of small devices. In this presentation, we use insects, Periplaneta Americana, as a power system to illustrate such effects.
10:30 AM - Z3.2
Thermoelectric Performance of Bulk and Nanostructured Zr0.5Hf0.5Co1-xIrxSb0.99Sn0.01 Half-Heusler alloys.
Nathan Takas 1 2 , Hongfang Zhao 1 2 , Pranati Sahoo 1 2 , Paul Schilling 3 , Pierre Poudeu 1 2
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States, 3 Department of Mechanical Engineering, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractSeveral samples with general composition Zr0.5Hf0.5Co1-xIrxSb0.99Sn0.01 (x = 0.0-0.7) were synthesized by high temperature solid-state reaction and the thermoelectric properties of the hot-pressed pellets were measured in the temperature range from 300K to 800K. Well mixed high purity powders of the starting materials, weighed in the appropriate stoichiometry, were vacuum-sealed in silica tubes and annealed at high temperature for several days. Several grinding and reheating cycles were necessary to achieve pure phases. The thermoelectric performance of the samples was optimized by the introduction of nickel oxide nanoparticles prior to the hot pressing of the samples. The effect of the nanoparticle inclusions as a function of mass percent inclusion was examined. All samples show p-type semiconducting behavior in the measured temperature range. Thermopower values on the order of 140 μW/K and electrical conductivity of about 150 S/cm have been observed at room temperature for samples prepared without inclusions. X-ray microtomography (Micro-CT) and scanning electron (SEM) microscopy studies of selected specimens are used to elucidate the microstructure of the materials. Thermoelectric properties of hot-pressed pellets of Zr0.5Hf0.5Co1-xIrxSb0.99Sn0.01 and the effects of Co/Ir ratio, the pressing parameters and the proportion of metal oxide nanoparticle inclusions on the properties of the materials will be discussed.
10:45 AM - Z3.3
Thermoelectric Properties of Solution-Processed Bismuth Chalcogenide Compounds.
Robert Wang 1 , Joseph Feser 2 , Xun Gu 2 , Rachel Segalman 1 2 , Arun Majumdar 1 2 , Jeffrey Urban 1 , Delia Milliron 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , University of California, Berkeley, California, United States
Show AbstractSolution-processed thermoelectric materials could lead to the widespread use of low-cost thermoelectric coolers and power generators. We present a simple wet chemistry route to precursors to the bismuth chalcogenides Bi2Te3, Bi2Te2Se, Bi2TeSe2, and Bi2Se3. These precursors can be dispensed using traditional solution-processing techniques and then thermally decomposed into a polycrystal of their respective compound. Preliminary room temperature measurements of spin-cast films demonstrate promising results with power factors ranging from 50 - 500 μW m-1 K-2. Our synthesis route is also amenable to doping and alloying, which we anticipate will lead to further improved performance.
11:30 AM - Z3.4
Influence of Lead Content on the Properties of Hot Pressed n-type Ag0.86PbxSbTe20(LAST).
Nuraddin Matchanov 1 2 , Jonathan D Angelo 1 , Chun-I Wu 1 , Muhammad Farhan 1 , Timothy Hogan 1 , James James Barnard 3 , Chuck Chuck Cauchy 3 , Terry Hendricks 4 , Joseph Sootsman 5 , Mercouri Kanatzidis 5
1 Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States, 2 Crystal Growth Laboratory, Physical Technical Institute of Uzbek Academy of Sciences, Tashkent Uzbekistan, 3 , Tellurex Corporation, Traverse City, Michigan, United States, 4 Pacific Northwest National Laboratory, MicroProducts Breakthrough Institute, Corvallis, Oregon, United States, 5 Chemistry Department, Northwestern University, Evanston, Illinois, United States
Show AbstractThe influence of the lead content on the thermoelectric properties of hot pressed n-type Ag0.86PbxSbTe20(LAST) materials prepared by Tellurex Corporation were investigated in the temperature region 300-750K. For the samples with lead content greater than nineteen 19 < x < 22 (Ag0.86PbxSbTe20) the sign of the thermoelectric power shows a p-type to n-type transition in the studied temperature region, and the temperature dependent electrical conductivity exhibits activated behavior. Temperature dependent thermal conductivity will also be presented along with Hall effect measurements. The power factor for the higher lead content samples shows low values near 300K and rapidly increases to ~20 (µW/cm K2) at 750K. For samples with all three measurements taken on the same sample, the figure of merit, ZT, as high as 1.2 at 700K was measured.
11:45 AM - Z3.5
Thermoelectric Behaviors of Polymer Nanocomposites by Changing Stabilizers and Drying Conditions.
Kyungwho Choi 1 , Yeonseok Kim 1 , Dasaroyong Kim 1 , Jamie Grunlan 1 , Choongho Yu 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractThis paper demonstrates that thermoelectric properties of carbon nanotube (CNT)-filled polymer composites can be altered by modifying the junctions between CNTs, increasing electrical conductivity dramatically up to ~12400 S/m without significantly altering thermopower (or Seebeck coefficient) and thermal conductivity. The decoupled thermoelectric properties, which have been extremely difficult to achieve in inorganic bulk semiconductors, are believed to be from thermally difficult and electrically connected contact junctions between CNTs. In this type of polymer composites, stabilizers can be sandwiched at the junctions between CNTs and polymer emulsion particles, playing an important role in transporting energy carriers. The crucial role of stabilizers was revealed by performing a series of experiments with composites synthesized by different type and amount of stabilizers that alter the junction properties. Additionally, the influence of composite synthesis temperature on thermoelectric properties has been studied. The outcome from systematic and comparative studies would be a basis for developing economical, light-weight, and efficient polymer thermoelectric materials in the future.
12:00 PM - Z3.6
Thermoelectricity in Doubly Doped Strontium Titanate.
Wolter Siemons 1 , Jayakanth Ravichandran 2 , Matthew Scullin 3 , Dongwook Oh 4 , Yee Kan Koh 4 , Herman Heijmerikx 6 1 , David Cahill 4 , R. Ramesh 2 3 , Arun Majumdar 3 5
1 Department of Physics, University of California at Berkeley, Berkeley, California, United States, 2 Applied Science and Technology Graduate Group, University of California at Berkeley, Berkeley, California, United States, 3 Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California, United States, 4 Department of Materials Science and Engineering, University of Illinois, Urbana-Champaign, Illinois, United States, 6 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands, 5 Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States
Show AbstractLanthanum doped Strontium Titanate (SrTiO3) is amongst the most promising n-type thermoelectric materials for power generation [1]. We report a double doping method for thin films of SrTiO3, grown on (001) oriented LSAT substrates by Pulsed Laser Deposition (PLD), where doping of SrTiO3 in the A-site by Lanthanum is accompanied by doping with oxygen vacancies. In the past theoretical predictions [2,3] showed that introducing oxygen vacancies in SrTiO3 produces a high-effective mass defect band just below the conduction band edge, validating the high seebeck coefficient observed in oxygen deficient SrTiO3 [4]. Based on careful transport measurements, we show that it is possible to obtain enhanced thermoelectric power factor by double doping, in the limit of high effective mass and large carrier concentration, in these thin films. With aid of optical spectroscopic measurements, we establish the presence of the impurity band created by the vacancies and validate their role in the enhanced thermoelectric performance with structural and transport measurements. The presence of oxygen vacancies also serves to decrease the thermal conductivity due to effective phonon scattering. Acknowledgements:We acknowledge Dr. Mark Huijben, Dr. Subroto Mukerjee and Dr. Choongho Yu, who have also made significant contributions to this work. We would like to acknowledge support from Department of Energy and Industrial Technology Research Institute, Taiwan.References:1. T. Okuda, K. Nakanishi, S. Miyasaka and Y. Tokura, Phys. Rev. B 63, 113104 (2001). 2. W. Wunderlich, H. Ohta and K. Koumoto, arXiv:cond-mat/0510013.3. W. Luo, W. Duan, S. G. Louie and M. L. Cohen, Phys. Rev. B 70, 214109 (2004).4. H. P. R. Frederikse and W. R. Hosler, Phys. Rev 161, 822 (1967).
12:15 PM - Z3.7
Thermoelectric Properties of Bi2Sr2Co2Oy Thin Films Grown by Pulsed Laser Deposition.
Jayakanth Ravichandran 1 , Wolter Siemons 2 , Herman Heijmerikx 3 , Joseph Feser 4 , Arun Majumdar 4 5 6 , R. Ramesh 5 2 6
1 Applied Science and Technology Graduate Group, University of California, Berkeley, Berkeley, California, United States, 2 Department of Physics, University of California, Berkeley, Berkeley, California, United States, 3 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands, 4 Department of Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 5 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 6 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractEpitaxial, c-axis oriented thin films of Bi2Sr2Co2Oy were grown on c-plane sapphire substrates by Pulsed Laser Deposition method. The thermoelectric properties of the films namely thermopower, electrical and thermal conductivities were measured over a temperature range of 300-700 K. The effect of the growth parameters on the thermoelectric properties is discussed. Magnetic measurements and X-ray Photoemission Spectroscopy (XPS) were performed to determine the valence and spin states of Cobalt and the validity of Heikes formula is checked for this compound.
12:30 PM - Z3.8
Towards thermoelectrics of electrodeposited lead telluride nanowires
Yongan Yang 1 , David Taggart 1 , Fan Yang 1 , Shing-Chin Kung 1 , Chengxiang Xiang 1 , Mattew Brown 1 , John Hemminger 1 , Reginald Penner 1
1 Chemistry, University of California, Irvine, Irvine, California, United States
Show AbstractWe report the synthesis and thermoelectric properties of PbTe nanowires made by an electrodeposition method. Thermoelectric materials could contribute to the efficient conversion of waste heat into electricity if the dimensionless figure-of-merit (ZT=S2σT/k) could be increased from the present value of 0.8 (400K) to 3.0. Theoretical calculations predict that one-dimensional thermoelectric materials (i.e., nanowires) should show a remarkable enhancement of ZT. Experimental verification of this enhancement has been slow in coming for PbTe and other compound materials because of the significantly practical difficulties associated with measurement of ZT for nanowires. In this presentation, we describe an efficient synthesis method—lithographically patterned nanowire electrodeposition (LPNE) for synthesizing PbTe nanowires. The PbTe nanowires prepared by LPNE are rectangular in cross-section with a width and height that can be independently controlled over the range from 60 to 500 nm and from 10 to 100 nm respectively, and they are electrically continuous up to millimeters. LPNE facilities the measurement of parameter including the electrical conductivity, σ and Seebeck coefficient, S, as a function of temperature and we shall report these data as well. The structure and chemical composition of the nanowires have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A method for suspending long sections of PbTe nanowires across an air gap – a capability that is crucial for measurement of thermal conductivity - will also be described. Ag-doped PbTe nanowires synthesized by LPNE demonstrate tunable thermoelectric properties due to the modification of the carrier type and concentration.
Z4: Advanced Energy Harvesting Systems
Session Chairs
Tuesday PM, December 01, 2009
Room 206 (Hynes)
2:30 PM - Z4.1
Computational Studies of Molecular-Level Effects Induced by Electric Fields Generated by Shaped Electrodes at the Nanoscale for Energy Storage Applications.
Alyson Niemeyer 1 2 , Neil Henson 1 , Albert Migliori 1 , Franky So 2
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Materials Science and Engineering, Univeristy of Florida, Gainesville, Florida, United States
Show AbstractElectrosynthesis, or the chemical generation of fuels by electricity, offers a pathway to the efficient storage of electricity generated by intermittent resources such as wind and solar power. The coupling of electric fields with nanoscale shaped electrodes provides a promising method to access alternative thermodynamic and kinetic chemical mechanisms to standard electrochemical conversions. This work uses quantum chemical methods on simple geometric models to examine the enhancement in the bond breaking process for several diatomic molecules. Density functional theory calculations using the B3LYP hybrid functional have been performed on a carbon monoxide (CO) molecule in an applied electric field. The field was created by charged electrodes consisting of point charges shaped as a plate or hollow sphere. It was found that that the CO bond breaks at an applied field of 98.5V/nm in a uniform axial electric field; and in a field created by a sphere and plate the CO bond breaks at an applied field of 74.0V/nm, which is 25% lower than the former scenario. The energies of the molecular orbitals were studied during the bond breaking and it was found that the pi orbitals, originally at a lower energy, switch energy levels with the sigma orbitals as the bond breaks. Similar behavior was found for the dinitrogen (N2) molecule. The polarization of the electron density was also investigated and results are shown. In addition the to the calculations from the sphere and plate electrodes comprised of point charges, an analytical solution for the potential distribution and electric field of a solid spherical shell was derived for comparison. Also described here are molecular dynamics simulations of supercapacitors based on carbon nanotube forests modeled at a molecular level. Results from calculations focusing on the electronic and ionic response of the nanotube-electrolyte assembly in the presence of an applied electric field are presented. Since the various factors included in these simulations are precisely defined, these results can be helpful in disentangling distinct physical factors which contribute to the performance of these materials.
2:45 PM - Z4.2
Advanced Computational Design of Intermediate-Band Materials for Hight-Efficiency Solar Cells.
Irene Aguilera 1 , Perla Wahnon 1 , Kefren Sanchez 1 , Pablo Palacios 1
1 Instituto de Energia Solar and Tecnologias Especiales Aplicadas a la Telecomunicacion, Universidad Politecnica de Madrid, ETSI de Telecomunicacion, Madrid Spain
Show AbstractIntermediate-band materials represent one of the most promising proposals in the quest of more efficient, lower-cost solar cells. We present here compounds derived from some families of semiconductors, namely chalcopyrites and spinels. In this compounds, some of the group-III atoms are substituted by transition metals to give rise to the intermediate band. These materials were proposed as high efficiency photovoltaic materials for intermediate-band (IB) solar cells. Calculations of TM-substituted semiconductors show a partially-filled band placed inside the band-gap which enables the absorption of photons with energies lower than the band-gap. This additional absorption could in principle increase the photocurrent of a cell, producing a significant effect on its performance. Due to the lack of experimental results of these materials, it is necessary for the proper understanding of the intermediate band formation, to study their properties theoretically in order to predict their suitability for high efficiency photovoltaic purposes. Our aim is to describe and predict by ab-initio methods their properties and especially the contribution of the new intermediate band to their absorption. For that purpose we need a precise description of the electronic structure of the systems and since this precision is not reached with standard DFT methods, the use of other advanced ab-initio methods is necessary. This work is thus devoted to understanding and analyzing in depth the optical and electronic behavior of intermediate-band materials with different advanced theoretical approaches and the comparison of several first-principles methods, in particular, GW, Time-Dependent Density Functional Theory (TD-DFT), DFT+U and hybrid functionals.A special attention is paid to the optical properties of M-substituted CuGaS2 and MgIn2S4 (with M=Ti,V). Absorption coefficients, reflectances, transmittances and band-to-band photoluminescence, are predicted for the IB materials and compared with those of the host semiconductors and their experimental data when available. Absorption spectra show a significant increase across the solar spectrum range, due to the transitions in which the intermediate band takes part.
3:00 PM - **Z4.3
Thermo-Magnetic, Piezo-Electric and Electroactive Energy Harvesting Devices.
Orphee Cugat 1 , Skandar Basrour 2 , Jerome Delamare 1 , Claire Jean-Mistral 2 , Louis Carlioz 1 2 , Maxime Defosseux 2 , Marcin Marzencki 2
1 G2Elab, CNRS / Grenoble-INP / UJF, St Martin d'Heres France, 2 TIMA, CNRS / Grenoble-INP / UJF, Grenoble France
Show AbstractWe present three approaches to harvesting ambient energy, based on complementary physical effects:1) Mechanical vibrations: an on-chip integrated prototype using a seismic mass on a Si cantilever beam coated with a piezoelectric AlN film (overall volume 5 mm3), produces 30 nW of rectified power at 3 V under 0.4 g acceleration, enough to power a wireless sensor. Power conditioning electronics adapted to ultra-low voltage input is also proposed, which can efficiently charge a storage capacitor under very low accelerations.Further progress requires a robust method of tuning the device's resonance frequency to match the dominant environment frequency: we propose a completely passive, wideband adaptive system based on mechanical nonlinear strain stiffening, obtained via high built-in stresses between deposited layers. Experiments show frequency adaptability of over 36% for a clamped-clamped beam under 2 g. The fully micro-fabricated System on a Package combines a MEMS generator and ASIC power management circuit.2) Low-frequency, large amplitude bending from human motion: a very light, flexible electroactive polymer membrane (area: 5x3cm, thickness: 31 μm) operates in a large frequency spectrum from quasi-static to dynamic range. It can scavenge 0.1mJ per cycle at 1 Hz, under 170 V and constant charge Q: 100 µW is enough to supply a low-power system.Real-life tests on a human are needed to determine the binding method and the impact of parasitic torsion. Improvements under investigation include achieving poling voltage with piezoelectric polymer or electrets polymer, using multi-stack scavengers to miniaturize the structure and to decrease the poling voltage V, and integration into textile.3) Evolutions of ambient temperature: a permanent magnet is attached to a PZT/brass bimorph, and placed near a "thermo-magnetic" material (FeNi) which Curie temperature can be tuned around the ambient (e.g. 45 °C). During slow cooling or heating by the ambient air, the FeNi magnetic properties vary and thus the attraction force between the FeNi and the NdFeB magnet varies. The opposition between the linearity of the bimorph's bending and the strong non-linearity of the magnetic attraction over distance leads to brutal clamping or release of the magnet around Tc: the piezo can then efficiently convert the fast deformations into electricity. Operational temperature range can be set by tuning the FeNi composition to obtain a predefined Curie point; hysteresis between the cooling/heating thresholds can be tuned by modifying the gap between the magnet and the FeNi.The cm-scale prototype generates a peak voltage of 35 V on release (T>Tc), (respectively -14 V on clamping), i.e. 1.35 mW (resp. 0.22 mW). For a discharge time of 0.1 s in a 1 MOhm load, the total energy is 13.5 uJ per stroke (resp. 2.2 uJ). Output power is surprisingly constant for various load values tested. Scaling effects must now be addressed to assess the efficiency of an integrated MEMS generator.
3:30 PM - Z4.4
Ideal Selective Surface Properties for Specific Applications.
Kenneth McEnaney 1 , Mildred Dresselhaus 2 , Gang Chen 1
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSelective surfaces are used in solar thermal applications to maximize the absorbed power and minimize losses. Selective surfaces have a high absorptivity in the visible range and a low absorptivity in the infrared range: a graph of absorptivity versus wavelength for an ideal selective surface is a step function. We focus on finding the optimal wavelength at which the step transition should occur. This optimal transition wavelength is driven by the specific application, as it is a function of solar insolation, surface temperature, optical concentration ratio, system losses, and the performance characteristics of the system to which the selective surface is attached. We present a methodology for finding the optimal wavelength, as well as a sensitivity analysis based on sample results for several systems. These data can help materials scientists design a selective surface for a given application. Acknowledgement: This work was supported by the DOE EFRC Solid-State Solar-Thermal Energy Conversion Center.
3:45 PM - Z4.5
Bio-Inspired Solar Energy Harvesting Based on Membrane Protein Functions.
Laura Pate 1 , Sarah McMurray 1 , Stephen Boyes 2 , Hongjun Liang 1
1 Materials Science, Colorado School of Mines, Golden, Colorado, United States, 2 Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado, United States
Show AbstractEnergy harvesting, conversion, and storage in living organisms is critically dependent upon membrane protein functions. Little is known on how to use these functions in practical devices. We are interested in integrating membrane protein functions into robust and addressable engineering materials. Proteorhodopsin is a membrane protein found in marine bacterioplankton that functions as a light driven proton pump. Using porous substrates with different pore sizes as supporting matrices, we show here that Proteorhodopsin can be reconstituted into lipid bilayers to form functional proteoliposome arrays that have defined protein orientation and packing density. Preliminary results on the performance of such composite membranes for solar energy harvesting will be discussed.
4:30 PM - Z4.6
Thermionic Emission Energy Distribution from Nanocrystalline Diamond Films for Direct Thermal-Electrical Energy Conversion Applications.
Kishore Uppireddi 1 4 , Tyler Westover 4 , Timothy Fisher 4 , Brad Weiner 1 3 , Gerardo Morell 1 2
1 Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 4 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 Department of Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show Abstract In the ongoing quest for energy production by non-conventional methods, energy conversion by vacuum and solid-state thermionic emission devices is one of the potentially efficient pathways for converting thermal energy directly into electrical power. Direct thermal-to-electrical vacuum thermionic energy conversion (VTEC) systems that can operate at moderate temperatures with high efficiencies provide the possibility of harnessing thermionic power conversion and for waste heat recovery applications. The unique advantages of VTEC technology are compactness, scalability, and high waste rejection temperatures for cascading systems [1]. The realization of practical of thermionic energy conversion devices strongly depends on achieving low work function materials, which is thus far a limiting factor. Previous efforts are limited by the non-uniformity in emitter work function and the higher temperature to obtain appreciable emission current. In an attempt to develop a new low work function thermionic material, this work reports thermionic emission energy distributions (TEEDs) from nanocrystalline diamond (NCD) films in the temperature range from 700 to 900°C that reveal a consistent effective work function of 3.3 eV. The NCD films also exhibit emission peaks corresponding to higher work functions as indicated by shifts in their energy position and relative intensity as a function of temperature. These shifts thus appear to be related to instabilities in the NCD’s surface chemistry. The results were discussed using energy level band motive diagram. The analysis of these data yields information on the origin of the low effective work function of NCD.1. T. S. Fisher, and D. G. Walker, J. Heat Transfer 124, 954 (2002).
4:45 PM - Z4.7
Solar and Thermoelectric Energy Conversion Based on Strongly Correlated Oxides.
Christian Jooss 1 , Gesine Saucke 1 , Steffanie Wiedigen 1 , Joerg Hoffmann 1
1 Institute of Materials Physics, University of Goettingen, Goettingen Germany
Show AbstractThe fast progress in processing nanostructured oxide materials enables the fabrication of interfaces with atomic level control over chemical structure. Such interfaces allow for systematically studying new mechanism of energy harvesting and conversion based on strongly correlated electron systems. Here, we present two case studies for evaluating the potential of strongly correlated oxides for solar and thermoelectric energy conversion. A solar cell was experimentally realized using n-doped SrTiO3 and a hole-doped Pr1-xCaxMnO3 (x=0.3), both materials exhibiting electron-phonon interaction. The hole carriers in the manganite form small polarons, which absorb light in the entire visible range due to excited polaron states and allow for multilevel excitation. In contrast, the electronic transport in the Nb-doped SrTiO3 is dominated by large polaron behavior. At room temperature, the solar cell shows an open circuit voltage of more than 200 mV. The photovoltaic properties strongly depend on the chemical structure of the interface. The temperature and spectral dependence of the photovoltaic energy conversion of light into electric power sheds light onto the role of electron-phonon and magnetic interactions on the conversion mechanism. Our second model system for studying energy conversion in strongly correlated oxides consists of slightly doped manganite-cobaltite multilayers. Both materials exhibit a significant Seebeck effect and represent interesting materials for high-temperature thermoelectric applications. We study electric and thermal transport properties in these multilayer systems in order to shed light onto the role of correlation effects at interfaces for enhancement of the Seebeck coefficient and for efficient decoupling of electric and thermal transport. This may offer new pathways for increase the thermoelectric efficiency.
5:00 PM - Z4.8
Minimum Length Scales of Power Factor Optimized Thermoelectric Nanostructures.
Paothep Pichanusakorn 1 , Prabhakar Bandaru 1
1 Materials Science, Mechanical Engineering department, University of California, San Diego, La Jolla, California, United States
Show AbstractThe inter-conversion of heat flow to electrical power via thermoelectric materials may enable waste heat recovery from many temperature activated processes and also lead to applications such as body-heat powered biomedical devices. However, practically the thermal-electrical conversion efficiency has been quite low (< 6%) in traditionally used bulk materials. Much excitement was then generated when it was theoretically proposed that the use of lower dimensional nanostructures such as quantum wells and nanowires could considerably boost the efficiency through a large enhancement of the power factor (S2σ : where S is the Seebeck coefficient and the σ the electrical conductivity). In this paper, we probe the fundamental limits of S2σ in terms of carrier concentration and length. Such considerations have enabled us to propose the existence of a universal, optimal S leading to the maximization of the S2σ in any material, at any temperature, and for any given dimensionality. We then show, through a critical comparison of the electron density distribution in the bulk and nanostructured forms for a variety of thermoelectrics, e.g., Bi2Te3, PbTe, SrTiO3, Si, and Si1-xGex etc. that there exists an optimal length scale only below which the S2σ of nanostructures is enhanced over the bulk value. It is then concluded that it is the increase in the magnitude of the integrated density of states (DOS) and not the change of shape, as is commonly believed, to be most responsible for the increase of the power factor. Our results lay the foundation for future research into the synthesis and characterization of nanostructured thermoelectric materials.
5:15 PM - Z4.9
Thermoelectric Module Measurement System.
Jonathan D'Angelo 1 , Naraddin Matchanov 1 2 , Chun-I Wu 1 , Timothy Hogan 1 , James Barnard 3 , Chuck Cauchy 3 , Terry Hendricks 4 , Mercouri Kanatzidis 5
1 Electrical Engineering, Michigan State University, East Lansing, Michigan, United States, 2 Crystal Growth Laboratory, Physical Technical Institute of Uzbek Academy of Science, Tashkent Uzbekistan, 3 , Tellurex Corporation, Traverse City, Michigan, United States, 4 Pacific Northwest National Laboratory, MicroProduct Breakthrough Institute, Corvallis, Oregon, United States, 5 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractMaterials of n-type Ag0.86PbxSbTe20 (LAST) and Ag0.9Pb9Sn9Sb0.6Te20 (LASTT) are among some of the best known thermoelectric compounds for the 600K – 800K temperature range. Technology transfer for further scale-up and device fabrication continues under this effort. Here we report on measurement systems used in the characterization of modules for output power versus load, and module efficiency. Materials developed for these modules were fabricated by Tellurex Corporation through a hot pressed fabrication procedure. The power output measurement system is a modular design where the sample space can be backfilled with an inert gas, and long term measurements can be taken. The efficiency measurement system is developed to accommodate the size of the modules for this project, and includes a double cold plate design to measure one or two modules at a time. The design and testing of these measurement systems and results from fabricated modules will be presented in this paper.
5:30 PM - Z4.10
Complete TEG Performence Measurement System.
Jan Koenig 1 , Ulrike Nussel 1 , Uwe Vetter 1
1 Thermoelectric systems, Fraunhofer IPM, Freiburg Germany
Show AbstractThermoelectricity is classified as one of the most promising technologies to exploit waste heat for the production of electrical energy. New individually optimized thermoelectric generator (TEG) modules are needed for special application in the low and high temperature regime (eg. automotive applications). A new TEG measurement system is developed to characterize the device performance. The idea behind this measurement setup is to combine a typical electrical measurement (generated voltage, electrical current, internal resistance and output power) with high resolution IR-thermography. The thermography is useful to get more insight in the complexity of thermoelectric systems and TEG-modules as the thermal resistance in the device can be detect in during operation. The temperature distribution and heat spreading in a TEG obtained with the thermal imagine setup can also be used to proof the simulation models that are used to optimize theoretically the TEG performance. The thermal resistance at contact is highly influenced by the contact pressure. The contact pressure changes with increasing temperatures while the material expands. To get measurement results that are independent of the measurement system the contact pressure is freely adjustable and it is also measured in-situ. To get an almost realistic measurement result close to applications the cold side temperature could be varied between 0°C and 130°C as it is common in many industrial and automotive applications. The maximum hot side temperature is 600°C. The measurement of some new high temperature modules is demonstrated here exemplary with this new TEG performance measurement system. The obtained results are presented and interpreted in consideration of device optimization.
5:45 PM - Z4.11
Segregated-Network Polymer Nanocomposites for Thermoelectric Energy Conversion.
Jaime Grunlan 1 2 3 , Choongho Yu 1 , Yeon Seok Kim 1 , Dasaroyong Kim 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Chemical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractThermoelectric systems are very effective in harvesting electricity from waste heat or heat sources with small temperature gradients relative to the environmental temperature. Polymers are intrinsically poor thermal conductors, a desired behavior for thermoelectrics, but low electrical conductivity and thermopower have prevented them from serious evaluation as thermoelectric materials in the past. The addition of carbon nanotubes to a polymer can bring it into the degenerate semiconductor or metallic regime. The present work demonstrates that nanotube-filled polymer composites can be viable for light-weight and economical thermoelectric energy conversion by using a segregated network approach. With the addition of 20 wt% single-walled carbon nanotubes, stabilized with poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) [PEDOT:PSS] in water, an electrical conductivity (σ) near 500 S/cm is achieved in a poly(vinyl acetate) [PVAc] matrix. When this conductivity is combined with a thermal conductivity (k) below 0.4 W/m K and thermopower (S) above 30 μV/K, a thermoelectric figure of merit (ZT = S2σT/k) of approximately 0.04 is achieved at room temperature. This is the first report of a polymer-based material with a ZT value greater than that of bulk silicon. It is believed that ZT greater than one is very possible with further work using this segregated network approach to building composite materials. This study suggests that polymeric thermoelectrics are possible and provides the basis for further development of lightweight, low-cost, and nontoxic polymer composites for thermoelectric applications.
Z5: Poster Session: Energy Harvesting
Session Chairs
James Holbery
Laura Lewis
Harry Radousky
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - Z5.10
Correlation between Microstructure and Thermoelectric Properties of Bismuth Telluride Thin Films Deposited by Co-sputtering.
Seong-jae Jeon 1 , Seungmin Hyun 2 , Bongkyun Jang 2 , Hak-Joo Lee 2 , Byung-Ik Choi 2 , Hoo-Jeong Lee 1
1 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 2 Division of Nano-Mechanical Systems Research, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of)
Show AbstractThermoelectric materials have been explored due to many applications in power generation and cooling devices. Specially, chalcogenides materials (Bi, Sb, Te) have good thermoelectric properties at room temperature. Those materials have been widely studied to improve thermoelectric properties with different processing methods. However, thin films of thermoelectric materials have not been heavily investigated.In this study, we present microstructure effect on thermoelectric properties of bismuth telluride films in the thickness of 500 nm. The films were deposited onto SiO2 coated Si substrates using a radio frequency (RF) magnetron co-sputtering system. The films were prepared from bismuth and tellurium targets at different substrate temperatures in the range between room temperature and 473 K. Post-annealing of the films was performed using a rapid thermal annealing system up to 673K under N2 atmosphere. We characterized the crystallinity and morphology of bismuth telluride films by using field emission scanning electron microscopy and x-ray diffraction. In further investigating the effects of the microstructure on the thermoelectric performance, the electrical mobility, seebeck coefficient and power factor of the film were evaluated. X-ray diffraction pattern of bismuth telluride films showed strong and sharp indication of Bi2Te3 (015) plane. Grain growth and surface morphology of the films were observed after thermal treatments. Carrier concentrations of the films were decreased while their mobility increased at large grained films after high temperature annealing. Seebeck coefficient and corresponding power factor of the film had their maximum value about –152 µV/K and 9.1x10-4 W/K2m, respectively. The correlation between microstructure and thermoelectric properties of bismuth telluride thin films will be presented and discussed.
9:00 PM - Z5.11
Nanocomposite of Bi2Te3/Bi0.5Sb1.5Te3 Alloys with Metal Nanoparticle Inclusions for Enhanced Thermoelectric Applications.
Sumithra Santhanam 1 , Nathan Takas 1 , Dinesh Misra 1 , Pierre Poudeu 1 , Kevin Stokes 1
1 AMRI, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractNanostructuring of bismuth antimony telluride (Bi0.5Sb1.5Te3) alloy, has recently been demonstrated, to improve the thermoelectric figure of merit (ZT) by upto 20-40% [1]. This nanostructuring approach increases phonon scattering due to grain boundary effect. A control over the grain size of the alloy matrix and densification of the alloy without significant grain growth can lead to a favourable grain boundary effect for phonon scattering and further lead to an overall increase in the ZT.In order to further improve the ZT in Bi0.5Sb1.5Te3 and Bi2Te3, by increased phonon scattering, we adopt a nanocomposite approach, wherein a secondary phase of metal nanoparticles act as nanoinclusion in the bulk alloy matrix. The alloy matrix has been synthesized by planetary ball milling and further densified by hot pressing. Appropriate quanitites of Bi, Sb and Te elemental shots were weighed in an Ar filled glove box and ball milled from 25 to 40 hours to achieve a single phase Bi2Te3 and Bi0.5Sb1.5Te3 alloy powders. Varying volume fractions of metal nanoparticles of bismuth and antimony (Bi,Sb) synthesized by a solvothermal method, were dispersed as a secondary phase into the alloy matrix. These composite powders were uniaxially hot pressed at 4000C, 50 MPa and properties compared to the pure alloys prepared under similar conditions. The effect of metal nanoparticles (nanoinclusions) on the thermoelectric properties has been quantified by measurement of the electrical resistivity, Seebeck coefficient and thermal conductivity from room temperature to 3000C. The effect of nanoinclusions on the charge carrier concentration and mobility of the nanocomposites, probed by Hall effect measurements, will also be presented. [1] B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M.S. Dresselhaus, G. Chen and Z. Ren, Science, 320, 634 (2008).
9:00 PM - Z5.12
Formation Behavior and Thermoelectric Properties of LnCuS2 (Ln: Pr, Nd, Sm and Gd).
Massoud Omar 1 , Toshihiro Kuzuya 1 , Shinji Hirai 1 , Michihiro Ohta 2
1 Material Science and Engineering, Muroran Institute of Technology, Muroran, Hokkaido, Japan, 2 Energy Technology Research Institute, AIST, Tsukuba, Ibraki, Japan
Show AbstractRare-earth copper sulfides also have layered structure, which consists of CuS4 and rare earth layers. Although it has been reported that some layered chalcogenides such as LaCuS2 and NdCuS2 have relatively high thermoelectric power (S) and relatively low electrical resistivity (ρ) at 300 K, the thermoelectric power factors are not satisfactory for utilizing these chalcogenides as thermoelectric materials. In this study, LnCuS2 (Ln: Pr, Nd, Sm and Gd) powders were synthesized by the following procedure: (1) a multiple oxide consisting of Ln and Cu was synthesized by the polymerized complex method, and (2) LnCuS2 was synthesized from this multiple oxide by the CS2 gas sulfurization. Furthermore the sintered compacts were produced by pulsed electric current sintering at a sintering temperature below their melting points. Then, the formation behavior and thermoelectric properties of LnCuS2 were examined. The single phase of PrCuS2, NdCuS2, SmCuS2, and GdCuS2 could be formed via sulfurization of the mixture of Ln2CuO4 and CuO at 1173, 1173, 1348 and 1273 K, respectively. The impurity contents of oxygen and carbon in products depended on the sulfurization conditions. For example, the PrCuS2 powder was obtained with high purity contents of 0.07 mass% carbon and 0.073 mass% oxygen by the sulfurization at 1223 K. According to procedure (1), it is considered that LnCuS2 was synthesized by the following formation reactions: a mixture of Ln2CuO4 and CuO was formed by a reaction between nanosized Ln2O3 (derived from Ln2O2CO3) and Cu/Cu2O/CuO mixture. Further, according to procedure (2), LnCuS2 was formed from an intermediate product LnOCuS, which was produced by the reduction of Cu++ by S2- in the mixture of Ln2CuO4 and CuO. During sintering, the formation of a single phase of LnCuS2 was also confirmed in all the sintered compacts. Subsequently, the thermoelectric properties were measured. The electric resistivity of sintered compacts decreased with the increasing temperature, and the Seebeck coefficient increased with the increasing temperature. The thermoelectric power factors became significantly higher than those of conventional values and, in addition, increased with temperature. The differences between the values of the obtained thermoelectric power factors and standard values were considered to be due to the differences between the impurity contents of the LnCuS2 powders and sintered compacts.
9:00 PM - Z5.13
Effects of Rhodium on the Thermoelectric Performance of Zr0.5Hf0.5Co1-yRhySb0.99Sn0.01 Materials.
Pramathesh Maji 1 2 , Pranati Sahoo 1 2 , Nathan Takas 1 2 , Pierre P Poudeu 1 2
1 Advanced Materials Research Institute, Univeersity of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractThe effects of variation of Rh concentration on the thermoelectric properties of Zr0.5Hf0.5Co1-yRhySb0.99Sn0.01 (0≤ y ≤1) half-Heusler alloys were investigated in the temperature range from 300K to 800K. Several compositions were synthesized via high temperature solid-state reaction starting from high purity elements. Elemental starting materials weighed in the appropriate stoichiometry were thoroughly mixed under argon atmosphere, sealed under high vacuum in silica tubes and annealed at 900 °C for several hours. The reaction progression was tracked by X-ray powder diffraction and DSC measurements. Several grinding and reheating cycles were performed in order to produce single phase materials. Preliminary structural characterization data on several compositions with varying Co/Rh ratio confirm the formation of pure half-Heusler phases. Thermoelectric properties of hot-pressed pellets of Zr0.5Hf0.5Co1-yRhySb0.99Sn0.01 (0≤ y ≤1) samples in the temperature range from 300K to 800K and the effects of Co/Rh ratio and the pressing parameters on the thermoelectric performance of the materials will be presented.
9:00 PM - Z5.14
Phase Stability and Thermoelectric Properties of Half-Heusler Compounds (Ti,M)NiSn (M = Zr, Hf).
Takahiro Kenjyo 1 , Yoshisato Kimura 1 , Yoshinao Mishima 1
1 Materials Science and Engineering, Tokyo Institute of Technology, Yokohama Japan
Show AbstractThermoelectric materials play a key role for conserving energy and preserving the global environment. We are focusing on half-Heusler compounds MNiSn (M = Ti, Zr, Hf), excellent n-type thermoelectric materials composed of nontoxic elements, which can be used at around 1000 K to directly convert waste heat into clean electrical power. Advantages of MNiSn alloys are excellent electrical properties, i.e., large Seebeck coefficient and low electrical resistivity. On the other hand, relatively high thermal conduction is a disadvantage. The lattice thermal conductivity is reduced by substituting M site elements between Ti, Zr and Hf, which is called as the solid solution effect since the differences in atomic mass and atomic size in a solid solution effectively enhance phonon scattering. Moreover, microstructure of thermoelectric materials affects its performance. Our group reported that Zr and Hf are all proportion miscible in (Zr,Hf)NiSn while the phase separation between Ti-rich HH and Ti-poor HH is observed in (Ti,Zr)NiSn and (Ti,Hf)NiSn.In the present study, we have focused on the HH phase separation in (Ti,Zr)NiSn and (Ti,Hf)NiSn from two viewpoints. One is to reduce the lattice thermal conduction by the solid solution effect and two-phase HH microstructures. The other is to develop Ti-base HH thermoelectric materials for economical and ecological reasons. The objective of the present work is to establish the basis of thermoelectric material design for (Ti,M)NiSn systems (M= Zr, Hf) based on phase stability and microstructures. Effects of the substitution of Ti for Zr or Hf in ZrNiSn or HfNiSn on the thermoelectric properties were also investigated using single-phase alloys prepared by the directional solidification using the optical floating zone melting method. Phase separation of HH phases can be confirmed by scanning electron microscopy and powder X-ray diffraction (XRD). Broadening or splitting of diffraction peaks clearly observed in XRD profiles depending on alloy compositions. To measure chemical compositions of constituent phases and to determine the solubility limit, electron probe micro analyzer was used. It was evaluated that the solubility limit of Ti in ZrNiSn and HfNiSn is approximately 6 at% and 8 at%, and the solubility limit of Zr and Hf in TiNiSn is approximately 9 at% and 8 at%. It indicates that two-phase region is widely spread in between Ti-rich and Ti-poor HH phases where microstructural control by heat treatments would be available. Thermoelectric properties of single-phase (Ti,M)NiSn alloys were measured in a temperature range from 300 to 1073 K. Among the single-phase (Ti,M)NiSn alloys, (Ti0.15,Zr0.85)NiSn shows the excellent ZT value of about 0.8 at 790 K since it has a good balance of a high electrical power factor together with a reasonably reduced thermal conductivity by substituting Ti for Zr.
9:00 PM - Z5.15
Modeling and Characterization of Flexible Thermoelectric Modules by Finite Element Analysis.
Bongkyun Jang 1 , Seung-Woo Han 1 , Jung Yup Kim 1
1 Nano-Mechanical Systems Reasearch Devision, Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of)
Show AbstractThermoelectric devices have various applications for thermoelectric generators and coolers such as power generation system for recovering waste heat, thermoelectric refrigeration and on-chip cooling system of microprocessor [1, 2]. Recently, the flexible thermoelectric devices, which is utilized in wearable electronic devices and foldable mobile devices, have investigated by some researchers [3, 4]. In these researches, polymeric materials of polyimide or SU8 are used as substrate, and thermoelectric materials are deposited on the substrate. For the conventional thermoelectric structure in which thermoelectric legs are located vertically between the substrates, the length of the thermoelectric legs is limited since it is difficult to deposit the thermoelectric materials thickly by thin film deposition process. On the other hand, horizontal type of thermoelectric module in which thermoelectric legs are placed horizontally between the substrates, is able to maintain the difference of temperature between upper and lower substrates if the heat conduction is controlled to lateral direction through the thermoelectric legs. For the successful design, it is necessary to simulate the efficiency of each type of thermoelectric module. The governing equations to evaluate thermoelectric efficiency are constructed by considering Seebeck effect, Peltier effect in addition to electrical and thermal conduction equations. With these governing equations, finite element analysis is conducted and the efficiency of thermoelectric module is calculated. We compare the efficiency of vertical type of thermoelectric module with the horizontal one. It is assumed that these two types of module are fabricated on polyimide substrate, and p-type and n-type thermoelectric material are Sb2Te3 and Bi2Te3 respectively. We also investigate the polyimide-filled model of vertical and horizontal type of thermoelectric module in which thermoelectric materials are surrounded by polyimide. Although this model has disadvantage of thermoelectric efficiency due to thermal conduction through polyimide, it has high endurance from large external strain. These results of analysis are used as design information for various types of flexible thermoelectric module.[1] D. M. Rowe, et. al., Thermoelectrics handbook : micro to nano, CRC Press, 2005[2] I. Chowdhury, et. al., On-chip cooling by superlattice-based thin-film thermoelectric, Nature nanotechnology, vol. 4, 235-238, 2009[3] L. M. Goncalves, et. al., Fabrication of flexible thermoelectric microcoolers using planar thin-film technologies, J. Micromech. Microeng. Vol. 17, S168-S173, 2007[4] W. Glatz, et. al., Optimization and fabrication of thick flexible polymer based micro thermoelectric generator, Sensors and Actuators A: Physical, Vol. 132, 337-345, 2006
9:00 PM - Z5.16
Biomimetic Photoelectrochemical Complexes Capable of Self-regeneration for Solar Energy Conversion.
Moon-Ho Ham 1 , Ardemis Boghossian 1 , Jong Hyun Choi 1 5 , Esther Jeng 1 , Daniel Heller 1 , Aidas Mattis 2 , Timothy Bayburt 2 , Yelena Grinkova 2 , Adam Zeiger 3 , Krystyn Van Vliet 3 , Erik Hobbie 4 , Stephen Sligar 2 , Colin Wraight 2 , Michael Strano 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractNaturally occurring photosynthetic systems in plants are supported by elaborate pathways of self-repair that limit the impact of photo-damage and degradation. Despite advantages in stability and fault tolerance, synthetic photoelectrochemical systems have to date been invariably static. In this presentation, we demonstrate a complex consisting of two recombinant proteins, phospholipid and a carbon nanotube that reversibly assembles into a particular configuration, forming an array of 4 nm lipid bilayers housing light-converting proteins orientated perpendicular such that the hole conducting site is in close proximity to the nanotube conductor. The complex can reversibly self-assemble into this useful configuration, and disassemble to free components upon the addition of sodium cholate, over an indefinite number of cycles. The assembly is thermodynamically meta-stable and can only transition reversibly between free components and assembled state if the rate of surfactant removal exceeds about 10-5 sec-1. In the assembled state only, the complexes exhibit high photoelectrochemical activity using a dual Fe(CN)63-/ubiquinone mediator with external efficiencies near 40% that are repeatedly recoverable even after continuous cycles of disassembly and regeneration. By mimicking natural repair processes, such systems may lead to more robust and facile solar conversion systems.
9:00 PM - Z5.17
Direct Thermal-to-electric Energy Conversion Material of Environmentally-benign Mg2Si Synthesized using Wasted Si Sludge and Recycled Mg Alloy.
Yasuhiko Honda 1 , Tsutomu Iida 1 , Shiro Sakuragi 2 , Yutaka Taguchi 2 , Yohiko Mito 3 , Hirohisa Taguchi 1 , Yoshifumi Takanashi 1
1 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba Japan, 2 , Union Material Inc.,, 1640 Oshido-jyoudai, Tone-machi, kitasouma,Ibaraki Japan, 3 , Showa KDE Co.,Ltd.,, 5-17-14 Nishiikebukuro, Toshima-ku, Tokyo Japan
Show Abstract In order to perturb global warming and realize a sustainable global energy system, enhancements in the energy efficiency are required. One of the reliable technologies to reduce the greenhouse gas emissions and the consumption of fossil fuel which is attracting attention is thermoelectric technology, which can directly convert heat into electricity and consequently increase the energy conversion efficiency of power generation by combustion. Magnesium silicide (Mg2Si) has been identified as a promising advanced thermoelectric material operating in the temperature range from 500 to 800 K. Compared with other thermoelectric materials that operate in the same conversion temperature range, such as PbTe, TAGS (Ge-Te-Ag-Sb) and CoSb3, Mg2Si shows promising aspects, such as the abundance of its constituent elements in the earth’s crust and the non-toxicity of its processing by-products, resulting in freedom from care regarding prospective extended restriction on hazardous substances. Here we have tried to introduce reusing of industrial waste of Si sludge as a source material for Mg2Si, because the current product inversion rate of Si for semiconductor LSI devices remains at 25 to 30 %, while most of the remainder is disposed of as a waste; this is mainly discharged as sludge from grinding and polishing processes. It is possible that the reuse of this waste Si could be effective in both reducing the cost of source Si and in the reduction of industrial waste. On the other hand, recycled materials of standard lightweight magnesium alloys based on the Mg-Al-Zn-Mn system, such as AZ91 or AM50, were also introduced as a Mg source for Mg2Si synthesis. The concept of this work is a production of wasted heat recovery device using environmentally-benign Mg2Si by means of industrial waste and less pure recycled sources. The efficiency of a thermoelectric device is characterized by the dimensionless figure of merit, ZT=S2σT/κ, of its constituent thermoelectric material, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. As a target for practical use, ZT value exceed unity, which gives about 10 % conversion efficiencies, is expected. So far, we succeeded to obtain the Mg2Si with ZT=1.08 using rather pure Si (99.999% : solar grade) and Mg (99.95%) sources. In this article, we report multifarious fabrication processes in order to realize ZT value as high as unity and the detailed thermoelectric properties concerning Mg2Si initiated from reused Si sludge and the recycled Mg-alloy sources. In conjunction, we will also discuss the practical output-power characteristics of the samples with the formation of Ni electrodes by monobloc sintering. A tentative generated power density from the wasted heat at 773 K was ~2 KW/m2.
9:00 PM - Z5.19
Transmission Electron Microscopy Investigation of Bismuth Telluride-based Thermoelectric Bulk Nano-composite Materials for Correlation to Thermoelectric Properties.
Dinesh Misra 1 , Sumithra Sumithra 1 , Kevin Stokes 1 , Ferdinand Poudeu 1 , Heike Gabrisch 1
1 Advance Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractBismuth telluride-based thermoelectric materials are extensively used for generating thermoelectricity and cooling at temperatures below 400 K [1]. The efficiency of thermoelectric devices is determined by the material’s dimensionless figure of merit, defined as ZT= (S2σ/k) T, where S, σ, k and T are the Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature, respectively [2-4]. In the present work, the thermo electric properties of bismuth telluride based thermoelectric materials are optimized through variations of microstructure parameters, e.g. homogeneity and grain size of a solid solution matrix, and size, shape and distribution of second phase particles. Here we present the microstructural characterization of nanocomposites formed by dispersing Bi nano particles into Bi2Te3 compound or Bi0.5Sb1.5Te3 solid solution matrices. We follow size, shape and distribution of Bi particles and give a reasonable explanation for the observed thermal conductivity of the nanocomposites compared to the thermal conductivity of the corresponding Bi2Te3 and Bi0.5Sb1.5Te3 solid solution alloys. Both the large size distribution and the high dispersion of the nanocrystals are believed to favor for the scattering of a wide phonon spectrum (mid to long wavelength) leading to significant alterations of the lattice thermal conductivity which in turn may enhance the figure of merit (ZT). References: 1.J. Yang, T Aizawa, A. Yamamoto and T. Ohta, 2000 a & b. J. Alloys Compd. 309, 225–228 & 312,326-330.2.D. M. Rowe, Ed. CRC Handbook of Thermoelectrics (CRC, Boca Raton, FL, 1995).3.H. J. Goldsmid, Thermoelectric Refrigeration (Plenum, NewYork, 1964). 4.T. M. Tritt, Ed. Semiconductors and Semimetals, Recent Trends in Thermoelectric Materials Research: Part One to Three (Academic, San Diego, vol. 69 to 71, CA, 2001). *Corresponding author:
[email protected]9:00 PM - Z5.2
Development of La(Co, Ni)O3 Thin Film on Flexible Substrate for Thermoelectric Applications.
Wenyan Jiang 1 , Seung-Hyun Kim 1 , Angus Kingon 1
1 , Division of Engineering in Brown University, Providence, Rhode Island, United States
Show AbstractThermal management in printed wiring boards (PWBs) has been an eye-catching issue due to the increasing dissipative powder in higher performance processors. To address the problem, thermoelectric materials have been chosen to act as a convertor to harvest the thermal energy and convert it back into electrical powder. One approach to achieve this is embedding thermoelectric functionality into the ubiquitous PWB. Additionally, there is a desire to extend this capability to flexible electronics. Our objective is therefore to develop flexible substrate thermoelectric devices that can be integrated into the modern multifunctional PWBs and flexible electronics. Among various thermoelectric materials, perovskite-type lanthanum cobaltates (La(Co, Ni)O3) has displayed it’s thermal stability at high temperatures, as well as good thermopower performance, attractive for our thermoelectric device objectives. The research discussed in this paper focuses on the processing of thin film lanthanum cobaltate materials on flexible substrates by solving the compatibility problem between the thermoelectric materials and the substrate. We will report on processing-property trade-offs, the resultant properties of the thermoelectric thin films, and the device design approaches and the efficiencies achieved.
9:00 PM - Z5.20
Characterization of P(VDF-TeFE) Thin Films formed with Annealing in Electric Field.
Jong-Hyeon Jeong 1 , Hidemitsu Aoki 1 , Chiharu Kimura 1 , Takashi Sugino 1
1 Department of Electrical Electronic and Information Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract In order to fabricate a micro generator which is activated by acoustic wave on a level with human voices, we have studied on synthesis of a piezoelectric polymer film. Because of the nature of the source wave, the material of a membrane should be low density, low elasticity and compatible with MEMS processes. P(VDF-TeFE) (Poly-vinylidene fluoride and tetrafluoroethylene) (supported by Daikin Co.Ltd.) is quite suitable for the present application in PVDF series as piezoelectric polymer. Average mechanical parameters of P(VDF-TeFE) is lower than that of PVDF as show in Table 1. A resonant frequency of P(VDF-TeFE) is superior to that of the PVDF film to apply to the acoustic device activated with a human voice because elastic modulus of P(VDF-TeFE) is lower than that of PVDF. In this study, we have succeeded in formation of P(VDF-TeFE) thin films using the annealing process of with an electric field. It has been found that the molecular structure of the film modified by an electric field. We investigate the influence of an electric field on properties of the film. Using the 2-types of solvents such as Methyl-Ethyl-Ketone (MEK) and mixed solvent with MEK and N, N- Dimethylacetoamide (DMA), the P(VDF-TeFE) thin film was formed by spin-coating method on a surface of a Pt/Ta-deposited silicon substrate. The annealing process was carried out in 195°C with and without electric field of 1 MV/m. XPS and FTIR measurements were carried out for the samples formed with single solution and mixed solution of 4 and 10% concentrations. The films formed by annealing with an electric field are very different from that by annealing without electric field. An adhesion of the film was improved by DMA, and also, molecular structure of the film can be metamorphosed by the solvent. In the region from 284 to 285 eV of the XPS spectrum from the C1s core level, the signal intensity due to the C-C bond was changed with the electric field during the annealing process. Moreover the remanent polarization (Pr) was changed in proportion to a bias frequency. In the case of annealing with an electric field, a higher Pr was obtained compared with that by annealing without an electric field. And Pr was decreased with increasing frequency. In order to apply the P(VDF-TeFE) film to a micro generator as a piezoelectric membrane, we have carried out formation of the film with the annealing method in an electric field and with different types of solvents. Properties have also been investigated for the films formed with various conditions.
9:00 PM - Z5.3
Lithium Ion Intercalated TiO2 Nanotube Arrays: Amplification of Photocurrent Generation.
Ben Meekins 1 , Prashant Kamat 1
1 , University of Notre Dame, Notre Dame, Indiana, United States
Show Abstract TiO2 nanotube arrays prepared by anodic corrosion of Ti films are being used as a 1-D scaffold to anchor light harvesting assemblies. These TiO2 nanotube arrays consist of 50-100 nm diameter and 1-100 μm long tubes and become crystalline upon annealing. Their application in batteries, solar cells and sensors has drawn significant interest from the research community. However, because of the limited spectral match of the solar spectrum (<5%), the overall photoconversion efficiency for these systems remains quite low (<1%). Attempts have been made to dope with elements like nitrogen,1 carbon, and sulfur so that the photoresponse of TiO2 is extended into the visible, but this has yielded limited success in terms of efficiency enhancement. Incorporation of cations into the TiO2 lattice has now been attempted to enhance the photoelectric performance of TiO2 nanotubes. Cations such as H+ and Li+ are intercalated into TiO2 nanotube arrays when subjected to short term pulsing of the electrode to negative potentials (>-1.0V vs. Ag/AgCl) in an electrochemical cell. The intercalation process is visualized from the color change and can be followed by monitoring the absorption change using spectroelectrochemical methods. Both the duration and applied voltage dictate the amount of cation intercalation into TiO2 nanotubes. The intercalation of these small cations has a profound effect in enhancing the photocurrent generation under UV-light irradiation. We have also shown that the intercalation of these cations is stable even when subjected to potentials of up to +1.0V for 5 minutes. A nearly three-fold increase in the external quantum efficiency (IPCE) as well as overall power conversion efficiency was observed upon intercalation of Li+ ions into TiO2 nanotube arrays. The analysis of the Voc decay following termination of illumination shows the ability of accumulated electrons to survive for a long period of time in Li+ intercalated TiO2 nanotubes. The role of cation intercalation in improving the photocatalytic properties of TiO2 nanotube arrays will be discussed.
9:00 PM - Z5.4
Preparation of Sr-Ru-O System Ceramics by Spark Plasma Sintering with Fine Powder from Metal-Citric Acid Complex Solution.
Keishi Nishio 1 , Takuro Haraguchi 1 , Tomomi Okada 1 , Junichiro Takahashi 1 , Tsutomu Iida 1 , Kazuyasu Tokiwa 2 , Tohru Kineri 3 , Tsuneo Watanabe 2
1 Department of Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba, Japan, 2 Department of Applied Electronics, Tokyo University of Science, Noda-shi, Chiba, Japan, 3 Deparmtent of Applied Chemistry, Tokyo University of Science, Yamaguchi, Sanyoonoda-shi, Yamaguchi, Japan
Show Abstract Thermoelectric materials with high thermo-power, low resistivity, and low thermo-conductivity have been investigated. Oxide thermoelectric materials are thermally stable and are relatively less harmless than intermetallic compounds such as Bi2Te3. Many researchers have recently reported p-type semiconductors with layered metal oxides, i.e., Na-Co-O and Ca-Co-O, which have low resistivity and low thermo-conductivity. For example, Ca3Co4O9 consists of Ca2CoO3 and CoO2 blocks alternately stacked along the c-axis, forming a layered structure. Thus, the physical properties are highly two-dimensional in the a-b plane compared with along the c-axis. These materials also have very good thermoelectric properties. A nonstoichiometric compound, SrRuO3, has high p-type electrical conductivity, and an Sr-Ru-O system has been reported to form a Ruddlesden-Popper layered structure similar to that of the Na-Co-O system. A Sr-Ru-O system is thus well-suited for thermoelectric devices. We used the spark plasma sintering method with fine powder prepared from a metal-citric acid complex solution to prepare ceramics that consisted of SrRuO3 with a perovskyte structure and Sr2RuO4 with a Ruddlesden-Popper layered structure. A precursor solution was prepared with metal salts (RuCl3 H2O and Sr(OCOCH3)2 0.5H2O) as raw materials, C6H8O7 H2O as the chelating agent, and H2O. The precursor solution, consisting of Sr:Ru in a 1:1 ratio, was heated at 823 K for 5 h after drying at 353 K for 8 h to obtain the precursor powder. The solution was then heated at above 823 K, and single-phase SrRuO3 was obtained without the creation of any organic residue or SrCO3. A single-phase Sr2RuO4 was obtained from a solution with Sr:Ru in a 2:1 ratio by being heated to above 1273 K. This method enabled pure SrRuO3 to be obtained while using a lower temperature than that used in a conventional solid-state reaction. To obtain the ceramics, we placed the calcined powder in a graphite die and heated it to 1673 K at a rate of 200 K/min and then kept it at that temperature for 0 sec at a uni-axis pressure of 50 MPa and at a low gas pressure below 10 Pa. The obtained ceramics had low bulk densities that were 90 % of the theoretical density. The electrical conductivity, Seebeck coefficient and thermal conductivity of a SrRuO3 sample were measured by the standard four-probe method in a flowing He gas atmosphere between 323 and 861 K. The electrical conductivity of SrRuO3 was 1.84×105 S/m at 861 K, the Seebeck coefficient was 29.6 μV/K, and the thermal conductivity was 8.89 Wm-1K-1.
9:00 PM - Z5.5
Thermoelectric Generator From SiO2/SiO2+Au NanolayeredMultilayer Films Effected by MeV Si Ions Bombardment.
Satilmis Budak 1 , C. Smith 2 , M. Pugh 1 , H. Martin 1 , R. Hill 1 , K. Heidary 1 , C. Muntele 2 , D. iLA 2
1 Electrical Engineering, Alabama A.&M. University, NORMAL, Alabama, United States, 2 Center for Irradiation of Materials, Alabama A.&M. University, NORMAL, Alabama, United States
Show AbstractThis efficiency of the thermoelectric devices is limited by the properties of n- and p-type semiconductors. Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. The defects and disorder in the film caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We have prepared the thermoelectric generator device from SiO2/SiO2+Au multi-nano layered superlattice films using the ion beam assisted deposition (IBAD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package have been used to determine the stoichiometry of the elements of SiO2, Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardment has been performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.
9:00 PM - Z5.6
Light Propagation in Electrospun Titania Nanofibers.
Yuan-Nien Chen 1 , Yi-Hao Chang 1 , Tzung-Ying Shie 1 , Changshu Kuo 1 2
1 Department of Materials Science and Engineering, National Cheng Kung University, Tainan Taiwan, 2 Center for Micro/Nano Science and Technology, National Cheng-Kung University, Tainan Taiwan
Show AbstractTitania nanofibers were fabricated by an electrospinning technique using poly(vinyl pyrrolidone) (PVP) and titanium tetraisopropoxide (TTIP) as sol-gel formulas. Post-calcination process at 450C removed the organic contents and converted the as-spun PVP/TTIP blends to anatase titania nanofibers. Randomly deposited titania nanofibers acted as a light propagation matrix where the light scattering took place. Relatively-broadened scattering UV-vis spectra with variations in titania fiber diameters and deposition thicknesses were carefully examined. The wavelength with maximum scattering outputs ranged from 350 to 650 nm was highly depended on the diameters of titania nanofibers from 200 to 530 nm. The linear correlation between maximum scattering wavelengths and titania fiber diameters was found in good agreement with the Mie scattering theory. In addition, photocurrents and hydrogen productions of these titania nanofibers were measured under the UV irradiation. Both investigations confirmed the light propagation in electrospun titania nanofibers linearly increased with the deposition thicknesses, which also significantly improved the efficiency of irradiation energy conversions.
9:00 PM - Z5.7
X-ray Absorption Spectroscopic Study of the Local Atomic Structure of Bi2Te3/Sb2Te3 Superlattices.
Azzam Mansour 1 , Rama Venkatasubramanian 2
1 Systems and Materials for Power and Protection, NSWCCD, West Bethesda, Maryland, United States, 2 Center for Solid State Energetics, RTI International, Research Triangle Park, North Carolina, United States
Show AbstractBi2Te3/Sb2Te3 superlattices (SLs) are being developed for high performance thermoelectric devices. The SL films are grown on GaAs substrates using a novel low temperature metal-organic chemical vapor deposition method [1]. Significant enhancement in the figure of merit “ZT” at 300K from 0.9 for bulk Bi2Te3 to 2.4 for SL (p-type) has been achieved by controlling the transport of phonons and electrons across the SL plane [2]. A minimum in the lattice contribution to thermal conductivity was observed for a 20/40 and 10/50 Å Bi2Te3/Sb2Te3 SLs. The reduction in lattice thermal conductivity for the SLs was attributed to coherent backscattering of phonon waves at the SL interface [3]. For this model to work, the superlattice interfaces have to be structurally of high quality with minimum degree of structural disorder at the atomic level. We have used X-ray absorption spectroscopy (XAS) to investigate the local structure parameters (such as distance and disorder) of Sb and Bi in 20/40 and 10/50 Å Bi2Te3/Sb2Te3 SLs. XAS, with its element specificity and sensitivity to short-range order, enables local structure determination for both Sb and Bi. The local structure parameters for the SLs will be compared to those of Sb1.5Bi0.5Te3 alloy film, Sb2Te3 reference film, bulk Sb2Te3 powder, and bulk Bi2Te3 powder. Using temperature dependent measurements, we were able to separate static disorder from thermal disorder for the first few coordination spheres of Sb-Te/Sb and Bi-Te/Bi. We show that static disorders for Sb and Bi in the SLs are small and comparable to those of bulk material. The temperature dependence of thermal disorder was analyzed using the Einstein and Debye models for lattice vibrations. A comparison of the Einstein and Debye temperatures for the SLs with those of the alloy, reference Sb2Te3 film, bulk Sb2Te3 powder, and bulk Bi2Te3 powder confirmed that the thermal disorder properties for the SLs are similar to those of bulk materials. The low degree of static disorders for Sb and Bi are consistent with structurally high quality SL interfaces and, hence, provide additional support to conclude that the reduction in lattice thermal conductivity for the SLs is due to coherent backscattering of phonons at the interfaces.1. R. Venkatasubramanian, T. Colpitts, B. O’Quinn, S. Liu, N. El-Masry, M. Lamvik, Appl. Phys. Lett. 76(8), 1104 (1999).2. R. Venkatasubramanian, E. Silvola, T. Colpitts, and O’Quinn, Nature 413, 597 (2001)3. R. Venkatasubramanian, Phys. Rev. B 61(4), 3091 (2000).
9:00 PM - Z5.8
High-Throughput Screening for Combinatorial Thin Film Library of LaxFe4Sb12 Skutterudites.
Shu Hui Wang 1 , Wen-Hsuan Chao 1 , Hsin-Ming Cheng 1
1 , Industrial technology research Institute, Hsinchu Taiwan
Show AbstractIn this research, a feasibility study was evaluated by using combinatorial material library method. The microstructures and thermoelectric properties were investigated on LaxFe4Sb12 thin films prepared by co-deposition of FeSb3 alloy and La element on glass substrates in a magnetron sputtering facility. The crystalline phase and composition of skutterudite LaxFe4Sb12 thin films can be validly controlled which confirmed by X-ray diffraction (XRD) and energy dispersion spectrum (EDS). The influence of La(x) doping grandient distribution on the nanostructures and characteristics of thermoelectric materials were also investigated. The value of x in LaxFe4Sb12 film with a continuous gradient of La concentration was in the range of 0 to 6. The Seebeck coefficient of thin films slowly decreases as increasing La(x) contents. Furthermore, the resistivity of thin films was reduced rapidly while light doping. On the contrary, the crystalline structure was degrading and the non-stoichiometric FeSb3 alloy films were obtained while heavy doping. We suggest the excess La retard the crystallization of the skutterudite phase during Ostwald ripening. Consequently, the power factor (α2/ρ) calculated from the values of α and ρ for LaxFe4Sb12 are in the range of 1.1 to 6.75 μW/K2cm at 300K with a maximum value located at x = 1.14.
9:00 PM - Z5.9
Effect of Nanophase Inclusion on the Transport Properties of Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01.
Rumana Yaqub 1 , Nathan Takas 1 , Pranati Sahoo 1 , Pierre F Poudeu 1 , Kevin Stokes 1
1 AMRI, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractThermoelectric nanocomposite materials have shown potential for use in heat-to-electrical energy conversion applications. For these applications, the materials must meet the conflicting requirements of high Seebeck coefficient and electrical conductivity and low thermal conductivity. Incorporating nanostructures into host bulk matrix material significantly reduces thermal conductivity due to the grain boundary scattering of phonons. This effect has been shown to increase the thermoelectric figure of merit, ZT in the half Heusler compound ZrNiSn[1].Here, we investigate the effect of nanostructred inclusions in a more complicated half Heusler material. Nine samples with the general composition Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01 were synthesized by high temperature solid-state reaction. These compounds crystallize in the cubic MgAgAs structure type. The obtained Zr0.5Hf0.5Ni1-xPdxSn0.99Sb01 compound powders were mixed with different volume fractions of nanometer- sized NiO (synthesized by solvothermal method). Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01/NiO composites were pressed by uniaxial hot-press. Microstructure characterization of the composites was accomplished with x-ray powder diffraction and electron microscopy. Seebeck coefficient, electrical resistivity and thermal diffusivity were measured over the temperature range of 300 K-800 K.The thermoelectric dimensionless figure of merit was calculated from the parameters. The effect of NiO nano-particle inclusions and small amounts of Pd substitutional doping on the thermoelectric properties of Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01 composition will be presented. The properties of Zr0.5Hf0.5Ni1-xPdxSn0.99Sb0.01 densified by uniaxial hot press and spark plasma sintering will be compared.1. X.Y. Huang, Z. Xu and L.D. Chen Solid State Communications 130,181 (2004)
Symposium Organizers
Harry Radousky Lawrence Livermore National Laboratory/
University of California-Davis
James D. Holbery GridMobility LLC
Laura H. Lewis Northeastern University
Frank Schmidt EnOcean GmbH
Z6: Energy Harvesting Materials III
Session Chairs
Wednesday AM, December 02, 2009
Room 206 (Hynes)
10:00 AM - Z6.1
Thermoelectric Property Characterization of Core-shell SiGe Nanowires.
Choongho Yu 1 , Vinay Narayanunni 1 , Yunki Gwak 1 , Sang-Won Jee 2 , Hongjoo Yang 1 , Liang Yin 1 , Jung-Ho Lee 2
1 Mechanical Engineering, Texas A and M University, College Station, Texas, United States, 2 Materials and Chemical Engineering, Hanyang University, Ansan Korea (the Republic of)
Show AbstractThermoelectric properties like electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (k), and their variation with temperature (T) of core-shell nanowires are being investigated. The nanowires have a SiGe core and an SiO2 shell. In this work, we report thermal conductivities of SiGe alloy nanowires, which is the first such measurement to the best of our knowledge. The thermal conductivities of SiGe core-shell nanowires with core diameters of 96 nm, 109 nm and 177 nm were measured within a temperature range of 40K-450K. The thermal conductivities measured in this work, were strikingly low. The thermal conductivities of these SiGe alloy nanowires on an average, are ~20 times lower than that of Si nanowires, ~10 times lower than that of Ge nanowires, ~3-4 times lower than that of SiGe thin film, Si/SixGe1-x superlattice thin film and Si/SixGe1-x nanowire; and about 3 times lower than that of bulk SiGe alloy at 300K. This trend is observed almost throughout the temperature range. The low values of thermal conductivities are proposed to be mainly due to boundary phonon scattering as a result of small wire dimensions, and due to the effect of alloy scattering. Another possible reason proposed is the influence of the SiO2 shell in creating disorder in the atomic structure near the boundary, thus affecting the boundary scattering. In addition, Seebeck coefficient and electrical conductivity of the same nanowires are presented. The influence of core-shell effect, alloy scattering and boundary scattering effect in reducing the thermal conductivity of these nanowires opens up opportunities for tuning the thermoelectric figure of merit which can pave way to thermoelectric devices and materials with high thermoelectric conversion efficiencies in the future.
10:15 AM - Z6.2
Electron-phonon Interactions in Silicon Microwires under Extreme Electrical Stress.
Helena Silva 1 , Gokhan Bakan 1 , Ali Gokirmak 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractSilicon microwires are partially or fully melted by single μs high voltage pulses. SEM analysis shows that melting of n-type wires always starts from the lower voltage terminal even though the structure and the thermal boundary conditions are symmetric. This asymmetry is evidence of strong Thomson Effect which occurs when charge carriers travel along a temperature gradient in an otherwise uniform material. For a given material, Thomson effect is expected to become significant under large temperature gradients and large current densities, such as our case with temperature gradients greater than 106 K/cm and current densities greater than 107 A/cm2. Thomson heat can be absorbed or evolved depending on the relative directions of the electric current and temperature gradient and the sign of β (Thomson coefficient) which is determined by the temperature dependence of the thermopower S. Thomson heat results in an asymmetric temperature profile as heat is evolved in one side and absorbed in the other side of the wire. In general, S (and therefore β) has a complex temperature dependence which results from electronic convective and electron-phonon scattering components which dominate in different temperature regimes. Intuitively, the observed asymmetry indicates that electron-phonon scattering contributions to the thermopower dominate over the electronic convective heat contribution. Electronic convective heat would result in the hottest spot shifted towards the positive terminal, opposite to what we observe, as electrons enter from the cold pad and heat through the wire, cooling the negative terminal and carrying heat along the wire towards the positive terminal. Since electrons travel from the negative to positive terminal and phonons travel from the hot center towards the cold ends of the wire, electron-phonon interactions would result in reduced thermal and electrical conductivity on the negative side and enhanced thermal and electrical conductivity on the positive side, leading to a temperature increase in the negative side as observed in our case. Although these effects are expected to be negligible at high temperatures and high doping levels, they appear to dominate in our case, due to extreme temperature gradients and current densities that act as driving forces for carriers and phonons.We will present our experimental observations of strong thermoelectric effects in silicon wires under extreme electrical stress and how they compare to numerical models that include different contributions to the thermopower S(T). The current continuity and time-dependent heat conduction equations including thermoelectric transport are solved self-consistently for the electric potential and temperature in the 3D structure under applied electrical stress.
10:30 AM - Z6.3
Comparative Study of Co and Ni Contacts to Bi2Te3 Thermoelectric Materials.
Husam Alshareef 1 2 , Rahul Gupta 1 , Ka Xiong 1 , John White 3 , K. Cho 1 , Bruce Gnade 1
1 Materials Science & Engineering, University of Texas at Dallas, Richardson, Texas, United States, 2 Materials Science & Engineering, King Abdullah University of Science & Technology (KAUST), Thuwal Saudi Arabia, 3 , Marlow Industries, Dallas, Texas, United States
Show AbstractCo and Ni contacts were used as contacts to Bi2Te3 thermoelectric materials. Interfacial characterization of the two material systems Co/Bi2Te3 and Ni/Bi2Te3 reveals substantial difference in interfacial reactions. While in the Ni case, a thick NiTe layer on the order of few hundred angstroms is formed, a much smaller layer is found in the case of Co/Bi2Te3. The findings are confirmed by both transmission electron microscopy and grazing incidence x-ray diffraction. Furthermore, the stress measured in the Co/ Bi2Te3 and Ni/ Bi2Te3 systems upon heating and cooling is consistent with these observations. Density functional theory calculations have been carried out for the two systems. The calculations show that the Co/Bi2Te3 system is more stable than the Ni/Bi2Te3 system. In addition, the calculations also reveal that the NiTe2/Bi2Te3 interface is more stable than the Ni/Bi2Te3 interface. The contact resistance for the two systems was also measured using the TLM method and indicate that the Co/Bi2Te3 system is at least as good as Ni/Bi2Te3. These results collectively suggest that Co may be a suitable alternative to Ni as contact material to Bi2Te3 based thermoelectrics.
10:45 AM - Z6.4
Structure-Strain-Thermoelectric Property Relationships of Donor Doped Epitaxial SrTiO3 Thin Films for Thermoelectric Device Applications.
Masatoshi Ishii 1 , John Baniecki 1 , Kazunori Yamanaka 1 , Kazuaki Kurihara 1 , Tetsuya Kaneko 2 , Paul McIntyre 2
1 Advanced Materials Lab., Fujitsu Laboratories Ltd., Atsugi, Kanagawa, Japan, 2 Department of Materials Science and Engineering, Stanford University, Stanford , California, United States
Show AbstractThermoelectric materials have gained significant attention as energy-conversion materials in order to recycle waste heat from power plants, automobiles, and computers into usable electrical energy. While the first practical thermoelectric material (bismuth telluride alloy) was prepared nearly 40 years ago, only recently has there been progress in realizing thermoelectric materials with significantly improved efficiencies. Perovskite structure metal titanate oxide thin films, such as SrTiO3, have emerged as an important thermoelectric material candidate owing to the ability to nanostructure and manipulate defect concentrations in such materials. While film structure, defects (such as vacancies and dislocations), and strain have been suggested to influence thermoelectric properties of donor doped SrTiO3 thin films, a detailed understanding of the interrelationship between them remains poorly understood. In the presentation we will present the results of studies characterizing the nanostructure and inhomogeneous and elastic strain state of donor doped SrTiO3 (STO) thin films grown epitaxially by pulsed laser deposition on insulating SrTiO3 (001) single crystal substrates over a wide range of film thicknesses (20-200 nm) and growth conditions. Correlations between the film structure, strain state and the thermoelectric properties, such as Seebeck coefficient, will be presented and the role of structure, defects and strain on the thermoelectric performance of STO thin films discussed.
11:30 AM - Z6.5
Abundantly Occurring Oxide Minerals for Solar Cell Applications: A Case Study in Cuprite-based Thin Film Heterostructures.
Kavaipatti Balasubramaniam 1 2 , Lane Martin 1 2 , Steve Byrnes 1 3 , David Chang 2 , Kevin Matthews 2 , Kyle Garton 2 , Joel Ager 1 , Ramamoorthy Ramesh 1 2 3
1 Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California, United States, 2 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 3 Department of Physics, University of California, Berkeley, California, United States
Show AbstractNaturally occurring mineral oxides and sulphides, which are abundant in the Earth’s upper crust, offer an enticing alternative to traditionally studied semiconductors in energy applications. The onus is now on researchers to understand, engineer, and develop such materials to a point where they can be effectively used in photovoltaic applications. Focusing on oxide minerals, cuprite (Cu2O) is an archetype hole-doped semiconductor that possesses several interesting characteristics useful for solar cells production; wide abundance and low cost, non-toxicity, good mobilities, long minority carrier diffusion length, and a direct band gap of ~2 eV. The use of Cu2O in solar cells has been studied since the 1970s however, practical application of this material in solar cells has been limited because of the difficulty in consistently optimizing the electrical properties. In this presentation, we discuss the growth and study of structural, physical, and photovoltaic (PV) properties of Cu2O thin films grown by pulsed laser deposition. Epitaxial Cu2O thin films were obtained on (001), (110), and (111) SrTiO3 (STO) and (001) and (110) MgO single crystal substrates. Detailed x-ray diffraction and transmission electron microscopy studies of the cuprite films reveal single-phase, high quality films. Cuprite films were found to grow with different epitaxial relationships depending on substrate choice, pre-growth substrate treatment, and substrate orientation. Film continuity and morphology were established through scanning electron microscopy and atomic force microscopy investigations. Key to the success of such materials in PV applications is achieving the highest carrier mobilities and minority carrier lifetimes. Hole mobilities of these high-quality cuprite films were measured in a standard Van der Pauw setup and were found to be in the range of 50-100 cm2/Vs at room temperature. Utilizing heteroepitaxial growth, we have investigated the influence of deposition conditions (i.e., deposition pressure and temperature), thin film strain (i.e., substrate choice and film thickness), and substrate orientation on the evolution of the transport properties in these films. Finally, we will discuss initial results on the creation and study of the PV response of Schottky barrier and “all oxide heterojunction” PV device structures in comparison to the previously studied devices.Acknowledgements: This work was performed within the Helios Solar Energy Research Center, which is supported by the Director, office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
11:45 AM - Z6.6
Interface Studies of Nano-grain Boundaries using Novel Capacitance Technique for Thermoelectric Applications.
Qing Hao 1 , Yucheng Lan 2 , Bhaskaran Muralidharan 1 , Xiaoting Jia 3 , Mildred Dresselhaus 4 , Zhifeng Ren 2 , Gang Chen 1
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Physics, Boston College, Chestnut Hill, Massachusetts, United States, 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Physics and Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractElectron transport in nanostructured thermoelectric materials can be significantly affected by the interfacial electronic states. To better understand the charge carrier transport process across the grain interfaces, we have conducted interface capacitance measurements to learn how many charges are trapped on the grain boundaries inside nanocomposites. The electronic barrier height at the interface can also be derived from the measurement results. Such information is important for the detailed theoretical analysis of the interfacial charge transport and energy conversion processes. Although large amount work has been done using the technique to understand the defect states and the barrier height of polycrystalline silicon grain boundaries, the method has not been applied to thermoelectric materials. Challenges associated with application of the capacitance measurement technique to thermoelectric materials will be discussed.
12:00 PM - Z6.7
Thin Film Nanocomposites for Energy Harvesting Applications.
Otto Gregory 1 , Ximing Chen 1 , Gustave Fralick 2 , Vince Wnuk 3
1 Chemical Engineering, Univ. of Rhode Island, Kingston, Rhode Island, United States, 2 , NASA Glenn Research Center, Cleveland, Ohio, United States, 3 , Hitec Products Inc., Ayer, Massachusetts, United States
Show AbstractThin film nanocomposites comprised of NiCoCrAlY based refractory metals and alumina were successfully prepared as thermal barrier coatings, since the large number of interfaces between the ceramic and metallic phases lead to considerable phonon scattering and ultra low thermal conductivities. When these nanocomposites were optimized for electrical conductivity, they exhibited promising thermoelectric properties. By substituting the alumina phase in these nanpocomposites with wide bandgap oxide semiconductors such as indium tin oxide (ITO) and alumina doped zinc oxide (AZO), nanocomposites with extremely large and repeatable Seebeck coefficients were realized. This was achieved by sputtering from composite targets prepared by plasma spraying optimized mixtures of NiCoCrAlY powder and semiconducting oxide powder onto stainless steel backing plates. Sputtering was selected as the method of choice to deposit the nanocomposites, due the low deposition temperatures and the non-equilibrium nature of the process, which greatly reduced any tendencies for particle agglomeration. Thermoelectric powers as large as 9000μV/°C were achieved for ITO:NiCoCrAlY nanocomposites when they were cycled between 600 and 1000°C. Based on these results and preliminary 2d thermoelectric calculations, the thermoelectric powers observed for these thin film nanocomposites are large enough to be considered for energy harvesting applications in the gas turbine engine environment, where large temperature gradients exists between the tip and the root of turbine blades. Such thermoelectric devices, for example, could potentially be used to power active wireless sensors.
12:15 PM - Z6.8
Functionalization of Nanoporous Gold Films in Energy Harvesting Devices.
Oya Okman 1 , Jeffrey Kysar 1
1 Dept. of Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractNanoporous gold films (NPG) have been proposed to have potential applications in micro-devices due to their high surface area. The enhanced double layer capacitance of a NPG film and its responsiveness under the strain suggests a new area of application as a novel energy harvesting device. In this study, a new design concept is discussed for the incorporation of nanoporous gold thin films energy harvesting devices. Preliminary experiments demonstrate a significantly enhanced double layer capacitance of the NPG as compared plain gold surfaces. The variation of capacitance by induced strain is investigated. The feasibility of the design has been investigated under in terms of fabrication, functionality and efficiency.
12:30 PM - Z6.9
Improvement of the Thermoelectric Properties of the Chimney–Ladder Compounds in the Ru-Mn-Si System.
Norihiko Okamoto 1 , Tatsuya Koyama 1 , Kyosuke Kishida 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Materials Science and Engineering, Kyoto University, Kyoto, Kyoto, Japan
Show AbstractChimney–ladder compounds with the general chemical formula of MnX2n-m (n, m: integers) possess tetragonal crystal structures which consist of two types of sublattices; one composed of transition metal atoms (M) with the β-Sn structure and the other composed of group 13 or 14 atoms (X) with a helical arrangement along the tetragonal c-axis. The unit cell of the chimney–ladder structure is composed of n×M sublattices and m×X sublattices stacking along the c-axis with c-axis dimensions of cM and cX, respectively. The high-temperature (HT) phase of Ru2Si3 (ruthenium sesquisilicide) is one of the chimney–ladder compounds with n=2 and m=1. Recently we have found that the HT-Ru2Si3 phase is stabilized by substituting Ru with Mn so as to exist even at low temperatures in a wide compositional range of the Mn content (∼0.12 ≤ Mn/(Ru + Mn) ≤ ∼1.00). Compositional analyses indicate that the Si/M ratio gradually increases as the Mn content increases, and that the solubility region of the (Ru,Mn)Siy (1.5 ≤ y ≤ 1.75) sesquisilicide phase with the chimney–ladder structure is virtually on the line between Ru2Si3 and Mn4Si7. Transmission electron microscopy shows that the c-axis dimension of the Si sublattice (cX) increases with the increase in the Mn content whereas that of the M sublattice (cM) is almost independent of the Mn content. Interestingly, compositional variations are observed even in a single crystal grain of the sesquisilicide phase in directionally solidified samples. The M sublattice is considered to be structurally continuous at the interfaces which separate compositionally different regions while the Si sublattice is discontinuous. It is considered that the compositional interface hardly affects the electrical resistivity because the d electrons of Mn atoms play a major role in electrical conduction of Mn4Si7 while the interface may impede the phonon transport to reduce the lattice thermal conductivity because the c-axis dimension (as well as the density) of the Si sublattice is discontinuous. In the present study, we investigate how the density of the compositional interfaces varies upon annealing the directionally solidified crystals. We will present the results of the thermoelectric property measurements as a function of the density of the compositional interfaces.
12:45 PM - Z6.10
Enhanced Thermal Conductivity of Phase Change Materials Modified by Graphite Nanoplatelets.
Jinglei Xiang 1 , Lawrence Drzal 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractPhase change materials are considered as one of the most promising materials for thermal energy storage due to their high latent heat and small temperature variation during phase transition. Paraffin wax has attracted numerous attentions for its low cost, low vapor pressure, high latent heat, negligible supercooling and chemical inertness. However, one of the intrinsic disadvantages associated with paraffin wax and other organic phase change materials are their low thermal conductivity (0.2 to 0.3W/mK), which severely limited their rate of absorbing and releasing heat from and to the environment. Exfoliated graphite nanoplatelets (xGNP) prepared by microwave exfoliation and mechanical grinding have been successfully incorporated into paraffin wax to make a thermally conductive phase change material to store thermal energy. In this work, xGNP particles are either randomly dispersed into paraffin matrix by melt mixing or preferentially aligned by two roll milling. Particles of different sizes (xGNP-15 and xGNP-1, abbreviated for the average lateral dimension of the particles to be 15um and 1um with thickness around a few tens of nanometers) are mixed into the matrix to study the size effect for thermal conductivity and electrical conductivity improvement in paraffin at different weight concentrations. SEM inspection of the sample cross section suggests that the platelet like morphology of xGNP particles is preserved well during sample preparation and xGNP-15 nanocomposites have lower electrical percolation threshold (less than 1vol %) than xGNP-1 composites (3vol%). At the same nanofiller loading level (<5vol%), the thermal conductivity of the xGNP-15 composites is always higher than the xGNP-1 composites despite the fact that the absolute number of reinforcing xGNP-1 particles is much more than its xGNP-15 counterparts (around 200 times more). For paraffin/xGNP composites prepared by melt mixing, the through plane thermal conductivity increases to 1.33W/mK for xGNP-15 composites as compared to 0.544W/mK for xGNP-1 composites at 4vol%. The two roll milled nanocomposites with particles preferentially aligned in paraffin matrix show higher in plane thermal conductivity than through plane conductivity (1.6W/mK vs. 0.6W/mK at 5vol% xGNP/paraffin samples). It is believed that the heat transfer in the composite is largely limited by the interface between the xGNP and paraffin. Different methods have been proposed to reduce the thermal interface resistance by using nanofillers of different morphologies (xGNP-1 and xGNP-15 or MWCNT and xGNP-15) so that the smaller platelets or nanotubes could serve as additional pathways for phonon transport when they bridge the larger platelets. DSC and TGA study have shown that the rate for paraffin to absorb and release heat energy is slightly improved by xGNP particles and thermal stability of paraffin wax nanocomposite is enhanced by xGNP particles.
Z7: Integrated Energy Harvesting
Session Chairs
Wednesday PM, December 02, 2009
Room 206 (Hynes)
2:30 PM - Z7.1
A Thermophotonic Heat Pump.
Jani Oksanen 1 , Jukka Tulkki 1
1 , Helsinki univ. of Technology, Espoo Finland
Show AbstractElectroluminescent cooling of semiconductors is a theoretically well known [1,2], yet undemonstrated phenomenon in which an electrically excited semiconductor cools down by light emission. The main challenge in demonstrating electroluminescent cooling is that a large portion of the photons emitted within the LED crystal which has a high refractive index, typically n_{r}>3, are back scattered at the crystal/air interface and are thus unable to escape the diode. Another challenge of efficient electroluminescent cooling is the very low internal quantum efficiency of the small band gap semiconductors (ideally E_{g}\sim kT) which otherwise would be most efficient in converting carrier heat to light energy.We propose a new approach to electroluminescent cooling in which the emitted photons are intentionally absorbed within the same semiconductor crystal they were originally emitted in and in which the requirements of demonstrating and making use of electroluminescent cooling are significantly relaxed compared to conventional structures. The resulting device, the thermophotonic heat pump (THP), is a new solid state heat pump that uses light as the working fluid. It shares all the advantages of thermoelectric devices like small size, reliability and the lack of environmentally harmful fluids or gases.The THP is formed of two large area light emitting diodes enclosed in a semiconductor material with an effectively homogeneous refractive index. The diode on the cold side of the structure, the emitter, operates as aconventional light emitting diode. It emits photons which obtain their energy from an external power source as well as from the lattice heat of the diode. The diode on the hot side, the absorber, operates as a photovoltaic cell. It absorbs the photons emitted by the emitter diode and the received energy is released as heat and electrical energy.Ideally the THP structure allows heat transfer or heat energy to electric energy conversion at the Carnot efficiency. The realizable performance of the device depends critically on the magnitude of the losses introduced by nonradiative recombination and parasitic absorption in the structure. A prototype THP can be fabricated on a standard n-doped indium phosphide substrate by standard fabrication methods of microelectronics. According to our theoretical simulations the THP has potential to demonstrate a significantly higher coefficient of performance (COP) than the thermoelectric devices, particularly in low temperature cooling applications. In addition, the THP structure allows low thermal conductivity between the hot and the cold side, which is not possible with the thermoelectric technology. If the THP can reach the predicted optimal performance it may revolutionize common cooling and heating applications ranging from refrigerators to household heat pumps.[1] Dousmanis, G.C. et al. Phys. Rev. 133, A316(1964)[2] Keves, R.J. & Quist, T. Proc. of the IRE 50, 1822-1856(1962)
2:45 PM - Z7.2
Advanced Soldier Thermoelectric Power System Operating from Tactical Quiet Generator Sources.
Terry Hendricks 1 , Tim Hogan 2 , Eldon Case 3 , Charles Cauchy 4
1 Hydrocarbon Processing Dept., Battelle Memorial Institute-Pacific Northwest National Laboratory, Corvallis, Oregon, United States, 2 Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States, 3 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States, 4 , Tellurex Corporation, Traverse City, Michigan, United States
Show AbstractThe U.S. military uses large amounts of fuel during deployments and battlefield operations. The true burdened cost of fuel delivered to the battlefield is very high. Consequently, the U.S. military has a strong need to develop technologies that increase fuel efficiency and minimize logistics trail and battlefield fuel requirements. There are additional requirements to minimize the environmental footprint of various military equipment and operations and reduce the need for batteries (non-rechargeable) in battlefield operations. The tri-agency SERDP (Strategic Environmental Research and Development Program) office is sponsoring a challenging, high-payoff project to develop a lightweight, small form-factor, soldier-portable advanced thermoelectric generator (TEG) prototype to recover and convert waste heat from a variety of deployed equipment (i.e., diesel generators/engines, incinerators, vehicles, and potentially mobile kitchens), with the ultimate purpose of obtaining additional power for soldier battery charging, advanced capacitor charging, and other battlefield power applications. The project seeks to achieve power conversion efficiencies of 10% (double current commercial TE conversion efficiencies) in a system with ~1.6-kW power output for a spectrum of battlefield power applications. In order to meet this objective, the project is taking on the multi-faceted challenges of tailoring LAST/LASTT-based thermoelectric (TE) materials for the proper temperature ranges (300 K – 700 K), fabricating these materials with cost-effective hot-pressed and sintered processes while maintaining their TE properties, measuring and characterizing their thermal fatigue and structural properties, developing the proper manufacturing processes for the TE materials and modules, designing and fabricating the necessary microtechnology heat exchangers, and fabricating and testing the final TEG system. The ultimate goal is to provide an opportunity to deploy these TEG systems in a wide variety of current military equipment (i.e., various Tactical Quiet Generator (TQG) systems) and battlefield operations so that they can provide the military with a pathway toward energy savings and environmental footprint management. This would help the Army in achieving one of the Office of Secretary of Defense’s major strategic objectives to maintain and enhance operational effectiveness while reducing total force energy demands. The presentation will review the progress made on 1) the performance of LAST / LASTT TE materials and tailoring their temperature dependency; 2) evaluating the structural (Elastic modulus, Poisson’s ratio and mechanical strength) properties of these materials, 3) development of the necessary LAST/LASTT-based TE modules, 4) development of the required hot- and cold-side microtechnology heat exchangers, and 5) the overall system designs for 30 kW and 60 kW TQG applications and potential performance pathways / differences for these two TQG cases.
3:00 PM - **Z7.3
Nanogenerators for Energy Harvesting.
Zhong Wang 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractDeveloping novel technologies for wireless nanodevices and nanosystems are of critical importance for sensing, medical science, defense technology and even personal electronics. It is highly desired for wireless devices and even required for implanted biomedical devices to be self-powered without using battery. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that will be used to power nanodevices without using battery. We have demonstrated an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire (NW) arrays. The operation mechanism of the electric generator relies on the unique coupling of piezoelectric and semiconducting dual properties of ZnO as well as the elegant rectifying function of the Schottky barrier formed between the metal tip and the NW. Based on this mechanism, we have recently developed DC nanogenerator driven by ultrasonic wave in bio-fluid. We have also used textile fibers for energy harvesting. This presentation will present our updated progresss in nanogenerators. [1] Z.L. Wang “Self-powering nanotech”, Scientific American, 298 (2008) 82-87.[2] Z.L. Wang and J.H. Song, Science, 312 (2006) 242-246.[3] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang, Science, 316 (2007) 102-105.[4] Y. Qin, X.D. Wang and Z.L. Wang, Nature, 451 (2008) 809-813.[5] R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang, Nature Nanotechnology, 4 (2009) 34-39.[6] Z.L. Wang “Towards self-powered nanosystems: from nanogenerators to nanopiezotronics” (feature article), Advanced Functional Materials, 18 (2008) 3553.[7] R.S. Yang, Y. Qin, C. Li, G. Zhu, Z.L. Wang “Converting Biomechanical Energy into Electricity by Muscle/Muscle Driven Nanogenerator”, Nano Letters, 9 (2009) 1201 - 1205.[8] for details: www.nanoscience.gatech.edu/zlwang
3:30 PM - Z7.4
Wideband Vibration Energy Harvester with High Permeability Magnetic Material.
Xing Xing 1 , Jing Lou 1 , Guomin Yang 1 , Ogheneyunume Obi 1 , Christopher Driscoll 1 , Nian-xiang Sun 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractA new vibration energy harvesting platform based on a high permeability magnetic cantilever beam was demonstrated, which overcomes the limitation of the existing approaches in output power and working bandwidth. The device consists of a vibrating high permeability cantilever, a solenoid and a bias magnet pair. The strong magnetostatic coupling between the vibrating highly permeable beam and the bias magnetic field leads to a maximized flux change in the magnetic beam and therefore a large induced voltage when the beam vibrates in the solenoid. The coexistence of magnetostatic and elastic potential energies leads to a wider potential well than those of the regular linear oscillators, resulting in a nonlinear oscillator with a wide bandwidth. The high permeability beam based energy harvester showed a high maximum energy of 74mW under an acceleration of 0.57g (with g=9.8m/s^2), a large time average energy density of 1.73mW/cm^3, and a wide bandwidth of 10 Hz (or 18.5% of the operating frequency). Compared to other vibration energy harvesting mechanisms, this high permeability energy harvester generates a set of very competitive figures of merit, which provides great opportunities for vibration energy harvesters that have high power output and wide working bandwidth.
3:45 PM - Z7.5
Thermoelectric Topping Cycle for Trough Solar Thermal Power Plant.
Andrew Muto 1 , Gang Chen 1
1 Mechanical, MIT, Cambridge, Massachusetts, United States
Show AbstractSolar thermal power generation is fast becoming cost competitive for utility scale electricity. Parabolic trough concentrators have proven economical and reliable but their efficiency is limited by the maximum temperature of the heated fluid. This work will explore the possibility of adding a thermoelectric power generator (TEG) as a topping cycle at high temperature to increase the overall efficiency of the system. In this design the perimeter of the receiver tube is covered with thermoelectrics so that the absorber temperature is raised and the energy rejected from the TEG is used to heat the original fluid. Heat transfer analysis is carried out on the design to determine the overall system efficiency.
4:30 PM - Z7.6
Design Principles for Nanopiezoelectric Energy Harvesting (NPEH).
Carmel Majidi 1 , Mikko Haataja 1 2 , David Srolovitz 3
1 Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States, 2 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 3 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractNanopiezoelectric energy harvesting (NPEH) has the potential to revolutionize the miniaturization of self-powered, wireless devices, sensors, and robots. In contrast to existing MEMS-based technologies for piezoelectric energy harvesting (PEH), NPEH is accomplished with an array of vertically aligned, single crystal, nanoscale cantilevers that convert mechanical strain to electricity through shear (15 mode) coupling [1]. This design avoids the need for heterogeneous, piezocrystal composites and can be readily fabricated with existing techniques. Because the individual crystals are nanosized, the complete energy harvesting device can be scaled down to a few cubic microns and potentially provide enough power to charge a battery, capacitor, or low-power device of comparable size.
Previous attempts at NPEH involved an array of zinc oxide (ZnO) nanowires that were reported to convert mechanical friction to electricity by sliding against an AFM tip [2]. Though promising, this method introduces the difficult task of requiring a single AFM tip to make near-simultaneous contact with both the leading and trailing edges of a bending nanowire. We propose a far simpler design for NPEH in which the nanowires are replaced by nanoribbons in which the piezoelectric poling direction is perpendicular to the long ribbon axis such that shearing creates a voltage drop across the length rather than the thickness. In this way, electricity can be harvested by forming a contact with a single point on the tip instead of with two opposite sides. Energy harvesting can also be accomplished by permanently bonding electrodes to the two sides of the cantilever array and attaching a proof mass on the top electrode. In this case, electricity is converted not from sliding friction but from the transverse vibration of the proof mass. This method of energy harvesting is analogous to, but distinct from, current methods of vibrational energy harvesting that use piezoelectric cantilever composites [3].
The governing equations for piezoelasticity show that the ratio of stored electrostatic energy to the externally applied mechanical work is inversely proportional to the aspect ratio squared. Therefore, greater energetic efficiency is achieved with low aspect ratio cantilevers. Such cantilevers, however, will exhibit a high bending stiffness and large resonant frequency; this significantly limits the functionality of both frictional and vibrational energy harvesting Geometric and material design criteria are suggested that simultaneously satisfy the conditions for functionality and maximum power output. These design criteria are derived with a comprehensive analysis based on mechanics, electrostatics, continuum piezoelasticity, and circuit theory.
[1] Z. L. Wang, Materials Today 10, 20-28 (2007).
[2] Z. L. Wang and J. Song, Science 312, 242-245 (2006).
[3] S. R. Anton and H. A. Sodano Smart Mater. Struct. 16, R1-R21 (2007).
4:45 PM - Z7.7
Theoretical and Experimental Study on the Piezoelectric Unimorph Cantilever Energy Harvester: Effect of the Nonpiezoelectric-to-Piezoelectric Length Ratio.
Xiaotong Gao 1 , Wan Shih 2 , Wei-Heng Shih 1
1 Department of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractInterest in using energy harvested from the environment to power autonomous systems such as wireless sensor networks and portable devices has grown significantly in recent years. The energy sources for harvesting include solar energy, energy from air/liquid flows, vibration energy and energy harvested from temperature gradients. Among them, vibration energy is attractive as it is abundant and independent of weather, or day or night. Piezoelectric cantilevers have been shown to be effective in converting mechanical vibration to electricity. In this work, we examined the effect of the nonpiezoelectric-to-piezoelectric length ratio of a piezoelectric unimorph cantilever on its energy harvesting performance. Theoretically, we have obtained an analytical solution for the mechanical and electrical responses of a harmonically driven cantilever based on Euler-Bernoulli beam theory. Experiments were carried out using unimorph cantilevers consisting of a 0.127-mm-thick lead zirconate titanate (PZT) of the same length (5 cm) bonded to a 0.05-mm-thick stainless steel (SS) of a varied length. Both theory and experiments showed that optimal PZT/SS length ratio vary with the vibration frequency range. For vibration frequency > 55 Hz, cantilevers with a longer PZT exhibited the highest open-circuit induced voltage. For vibration frequency < 15 Hz, cantilevers with the PZT and SS of equal length gave the highest open-circuit induced voltage. Between 15 Hz and 55 Hz, cantilevers with a longer SS gave the highest open-circuit induced voltage. For the power dissipation on a resistive load, the cantilevers with the PZT and SS of equal length gave the highest power output at all driving frequencies. Furthermore, the voltage and power output of the cantilevers of different nonpiezoelectric-to-piezoelectric length ratios with a proof mass attached to the tip will be investigated.
5:00 PM - Z7.8
Modeling, Fabrication and Characterization of PZT-based MEMS Piezoelectric Mechanical Vibration Energy Harvesters.
Miso Kim 1 , Jung-Hyun Park 2 , Seung-Hyun Kim 3 , Angus Kingon 3 , Dong-Joo Kim 2 , Brian Wardle 1
1 Aeronautics and Astronautics, MIT, Cambridge, Massachusetts, United States, 2 Materials Engineering, Auburn University, Auburn, Alabama, United States, 3 Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractIn recent years, there has been a growing interest in MEMS piezoelectric vibration energy harvesting due to advances in low power digital signal processors. While many research groups have focused on the study of bulk prototypes of piezoelectric energy harvesting, only a few groups have demonstrated MEMS devices capable of generating useful power. In this work, a microelectromechanical system (MEMS) piezoelectric energy harvester is thoroughly investigated both theoretically and experimentally. First, a macroscopically-verified modal model based on electromechanical coupling and beam dynamics is used to not only propose a power-optimized design of a microscale mechanical piezoelectric vibration energy harvester device, but also to simulate the device performances. Additionally, in order to obtain a high-quality piezoelectric thin-film, Pb(Zr,Ti)O3 (PZT) sol-gel processing conditions are considered through the analysis of material properties. Then, based upon the optimal parameters from modeling and material property analysis, a PZT piezoelectric cantilevered energy harvesting device with a proof mass is micromachined and the performance of the device is experimentally evaluated. Both mechanical and electrical responses of the energy harvester device are compared with the modeling results for experimental verification of the model in microsystems. Progress on fabrication and testing of a PZT-based MEMS harvester is also discussed along with device performance improvements.
5:15 PM - Z7.9
Piezoelectric Vibration Harvesting Device with Resonance Frequency Automatic Tracking Capability.
Maxime Defosseux 1 , Marcin Marzencki 2 , Skandar Basrour 1
1 Micro-Nano-Systems, TIMA, Grenoble France, 2 Engineering Science, Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractThere is nowadays a huge interest for wireless sensor networks in industrial or natural environment. However, a challenge is still present to see these networks commonly used: having energy sources with infinite lifetime to replace batteries at each network’s nodes and avoid maintenance cycles. Piezoelectric ambient energy scavengers are a promising solution to this problem [1]. However, as these scavengers are resonant, their resonance frequency has to match the dominant frequency in the surroundings to be efficient. Unfortunately, fabrication and material properties scattering lead to variations on resonance frequency. As a consequence, an energy harvesting device with adaptable resonance frequency is needed to make this energy scavenging method more efficient [2].In this work, an innovative passive way of resonance frequency automatic tracking will be presented. We propose a new approach using mechanical non-linear behaviour of the system, so that the nonlinear system tracks the vibration frequency peak.Different types of piezoelectric harvesters with different nonlinearities have been studied. Nonlinearities for clamped-free beam and clamped-clamped beam with a piezoelectric layer will be presented, compared and explained physically for two different piezoelectric layers, AlN and PZT. These nonlinearities lead to a bending of the frequency response, and a resonance frequency shift, different for each piezoelectric material. For highly nonlinear devices such as clamped-clamped beam, a hysteresis appears in the frequency response for high accelerations, depending on the direction of frequency excitation sweep. Material properties play a strong role in the device behaviour, and high quality factor’s materials are needed to use this non linear tracking method. An analytical model of these non linear systems will be presented, supported with finite elements modelling, and will allow us to explain the behaviour of clamped-free beam and clamped-clamped beam, and the important parameters of such a nonlinear system. This analytical model is based on Duffing’s mechanical oscillator [3]. Experimental results obtained with custom fabricated MEMS devices will be presented, and an experimentally verified frequency adaptability of over 36% for a clamped-clamped beam device at 2g (1g=9.81m.s-2) input acceleration is reported. We believe that the proposed solution is perfectly suited for autonomous industrial machinery surveillance systems, where vibrations with high accelerations that are necessary for enabling this solution are abundant.References:[1] M. Marzencki and al, “Integrated power harvesting system including a MEMS generator and a power management circuit”, Sens. Actuators A, 2008.[2] S. Roundy and al, “Improving power output for vibration-based energy scavengers,” IEEE Pervas. Comput., vol. 4, 2005.[3] L. Landau and E. Lifshitz, Mechanics. Pergamon Press, 1976
5:30 PM - Z7.10
Maximal Energy That Can Be Harvested From A Dielectric Elastomer Generator.
Adrian Koh 1 2 , Xuanhe Zhao 1 , Zhigang Suo 1
1 School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Engineering Mechanics, Institute of High Performance Computing, Singapore, Singapore, Singapore
Show AbstractMechanical energy can be converted to electrical energy using a dielectric elastomer. Experiments have shown that dielectric elastomer generators (DEGs) can achieve energy conversion at a specific energy of 0.4 J/g per cycle of operation, which is more than an order of magnitude higher than piezoceramics and electromagnetic generators. A method was recently developed to calculate the maximal energy that can be harvested from an ideal DEG. It was based on the consideration of various electro-mechanical failure modes of dielectric elastomers. These failure modes define the boundaries of operation for a DEG, which can be plotted on a force-displacement plane, and a voltage-charge plane. The area bounded by these failure modes defines a cycle that gives the maximum energy that can be harvested from a DEG. Using representative material parameters for a VHB acrylic dielectric elastomer, theoretical maximum specific energies of between 3.0 J/g and 6.3 J/g were obtained. The specific value of the amount of energy harvested is dependent on the mechanical stretching mode. Energy harvested is at its maximum when stretched in the equal-biaxial mode, and at its minimum when stretched in the uniaxial mode. A simple, two-battery circuit was analyzed. The energy harvesting process of such a circuit is analogous to the Carnot-cycle of a heat engine. Energy harvesting design plots for this circuit were constructed for both the equal-biaxial, and the uniaxial stretching mode.