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:hgabrisc@uno.edu
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 b