Nini Pryds, Technical University of Denmark
Asaya Fujita, National Institute of Advanced Industrial Science and Technology (AIST Chubu)
Neil Mathur, University of Cambridge
Ichiro Takeuchi, University of Maryland
EE11.1: Session I
Tuesday PM, March 29, 2016
PCC North, 100 Level, Room 127 A
2:45 PM - *EE11.1.01
Magnetocaloric Effect: Where We Are Today and What Does the Future Hold
Vitalij Pecharsky 2,Karl Gschneidner 2,Yaroslav Mudryk 1,Durga Paudyal 1
1 Ames Laboratory, Iowa State University Ames United States,2 Materials Science and Engineering Iowa State University Ames United States,1 Ames Laboratory, Iowa State University Ames United StatesShow Abstract
Nearly twenty years old, the discovery of the giant magnetocaloric effect in Gd5Si2Ge2 and other R5T4 compounds (R = rare earth metal and T is a Group 14 element) generated a broad interest in the magnetocaloric effect and magnetic refrigeration near room temperature in particular, and magneto-structural transitions in general. Last decade has been also marked by rising interest in materials exhibiting strong electrocaloric, elastocaloric, and barocaloric effects. The rapidly increasing interest in calorics is related to the fact that residential and commercial cooling systems consume at least one out of every five kWh generated in the U.S., yet vapor-compression refrigeration asymptotically approaches its fundamental efficiency limit. Whereas system-level studies predict lower environmental impact and higher efficiency for solid-state, caloric-based cooling compared to the vapor-compression cycle, successful market penetration of the energy-efficient caloric cooling technologies is impeded by lack of sustained, coordinated effort to provide the missing basic knowledge on both how to design the most effective solids, and how to control the processes in solids that change their state and temperature under the influence of external magnetic, electric, pressure, or stress fields. A common feature observed in all materials that exhibit the giant magnetocaloric effect is the coupling of magnetic and elastic effects. In addition to the interplay between magnetic and lattice entropies, both of which are intrinsic materials’ parameters that in principle can be modeled theoretically from first principles, extrinsic parameters such as microstructure and nanostructure, have been found to play a role in controlling both the magnetostructural transition(s) and magnetocaloric effect. Both the intrinsic and extrinsic parameters are, therefore, important in order to maximize magnetocaloric effect. The role of different control parameters and the potential pathways towards materials exhibiting advanced magnetocaloric effect will be discussed.
Ames Laboratory is supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences of the U.S. Department of Energy under contract No. DE-AC02-07CH11358 with Iowa State University.
3:15 PM - EE11.1.02
Low Hysteresis Material for Future Applications
Vijay Srivastava 1
1 GE Global Research Niskayuna United States,Show Abstract
To increase the efficiency and functionality of future applications, a low hysteresis material is required. Within the class of material that goes through first order transition, widely known as shape memory alloy, enjoys widespread applications in the field of defense, medical industry and national security. Since last decade, multiferroic alloys that have more than one ferroic property (ferroelasticity, ferroelectric and ferromagnetic) have been considered for future material. We conjectured that by using two of the ferroic properties, these alloys can be exploited for alternate energy. Strategically, guided by theory, known as ‘Geometrically non-linear theory of martensite’, the series of low hysteresis alloy is discovered. The general strategy to achieve low hysteresis in big first order phase transformations will also be discussed. We demonstrated that hysteresis in structural phase transformations are dramatically influenced by interfacial compatibility. One of the interesting materials is equiatomic FeRh alloy with a magnetic phase transition exhibited around room temperature. This alloy is useful for many applications, such as magneto caloric, and a micro electrical mechanical system (MEMS) devices. The FeRh alloys have not been employed in any engineering applications because of large thermal hysteresis. The purpose of this study is to reduce thermal hysteresis with a relatively sharp magnetic transition. As discussed above, geometric non- linear theory is used to design the material to get small hysteresis in FeRh systems. The magnetic properties and thermal hysteresis of ordered bcc FeRh 1-x M x alloys (M=, Pd, Ir and Pt) were studied. In nutshell, a relationship between the hysteresis and the middle eigenvalue, λ2, of the distortion matrix was found. The size of the hysteresis dropped sharply near λ2 = 1. Both theoretically and experimentally, it is established that the condition λ2 = 1 is a necessary and sufficient condition for a perfect, untwinned interface between austenite and martensite.
3:30 PM - *EE11.1.03
Magnetocaloric Heat Pump Systems: An Overview
Steven Russek 1,Andre Boeder 1,Jeremy Chell 1,John Leonard 1,Carl Zimm 1
1 Astronautics Corporation of America Milwaukee United States,Show Abstract
In recent years caloric materials have gained increasing interest for application to alternative cooling and refrigeration systems. Caloric materials, magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric), are materials that undergo a thermal change under the application of an appropriate applied field (magnetic, electric or stress respectively). Amongst these materials magnetocaloric materials are perhaps the most extensively researched as are their application to cooling and refrigeration systems. In this talk, we discuss computational modeling and experimental aspects of the application of magnetocaloric materials to magnetocaloric heat pump systems.
4:30 PM - *EE11.1.04
Challenges in Going from 2nd Order to 1st Order Materials in Magnetic Refrigeration Devices
Christian Bahl 1,Kurt Engelbrecht 1,Dan Eriksen 1,Kaspar Nielsen 1,Tian Lei 1,Anders Smith 1,Nini Pryds 1
1 Technical University of Denmark Roskilde Denmark,Show Abstract
Magnetic refrigeration devices rely on the utilisation of the magnetocaloric effect (MCE) present in magnetic materials. For a ferromagnet, the MCE is maximised close to the Curie temperature. Thus in order to utilise the MCE in devices, a choice of materials must be made according to the value and tunability of the Curie temperature as well as the strength of the MCE. Materials with a first order phase transition in general have a higher magnetocaloric effect than those with a second order phase transition, but the operational temperature span is much narrower. This, and complications arising from hysteresis effects and structural stability issues, has driven device development to rely mainly on second order materials, with only a few using first order materials.
A compact and highly efficient, but also versatile, magnetocaloric prototype device has been constructed at the Technical University of Denmark . The performance of gadolinium alloys, all second order materials, will be presented. Based on this the path towards utilising first order materials in devices will be discussed in relation to materials properties and small scale testing.
It is well known that first order materials are often brittle and will easily break when repeatedly taken through the structural first order transition. This makes them challenging to process into the desired shapes, thus limiting the possibility of controlling the convective heat transfer and pressure drop properties of the solid structures. In addition, regenerator performance may be severely reduced if the morphology is not chosen to minimise the magnetostatic demagnetisation . Recent modelling work has demonstrated how the narrow peak in the magnetocaloric effect will make performance very sensitive to the accurate layering of the materials . A large number of materials and a very high precision in the Curie temperatures are required from the materials manufacturer to meet these needs. Also, even small values of hysteresis have been shown to have a severe impact on the performance of materials in devices . These issues and their implication on the device performance will be discussed.
 D. Eriksen, K. Engelbrecht, C.R.H. Bahl, R. Bjørk, K.K. Nielsen, A.R. Insinga and N. Pryds, Int. J. Refrigeration, 58, 14-21 (2015)
 K.K. Nielsen, A. Smith, C.R.H. Bahl and U.L. Olsen, J. Appl. Phys. 112, 094905 (2012)
 T. Lei, K.K. Nielsen, K. Engelbrecht, C.R.H. Bahl, H. Neves Bez, C.T. Veje, J. Appl. Phys., 118, 014903 (2015)
 L. von Moos, C.R.H. Bahl, K.K. Nielsen and K. Engelbrecht, J. Phys. D: Appl. Phys. 48, 025005 (2015)
5:00 PM - EE11.1.05
Advancements in Magnetocaloric Liquefaction
Jamie Holladay 1,Jun Cui 2,John Barclay 3,Kerry Meinhardt 1,Evgueni Polikarpov 1,Edwin Thomsen 1,Iver Anderson 4
1 Pacific Northwest National Laboratory Richland United States,2 Iowa State University Ames United States3 Emerald Energy Northwest LLC Redmond United States4 AMES National Laboratory Ames United StatesShow Abstract
The Pacific Northwest National Laboratory working with Emerald Energy Northwest, Iowa State University, and AMES National Laboratory has built and operated a reciprocal magnetocaloric gas liquefaction system for use with hydrogen and other gases. Magnetocaloric hydrogen liquefier (MCHL) technology promises cost-effective and efficiency hydrogen liquefaction because it eliminates compressors, the largest source of inefficiency in the traditional Claude-cycle liquefiers, and the need for liquid nitrogen to pre-cool the hydrogen or other gases. While designed for hydrogen, the same configurations can be used for natural gas and other gases.
The MCHL system was tested over a range of conditions and with two types of dual regenerators. The first type regenerator used ~1kg of Gd material in each of the dual regenerators. Under a 3T field and no load, a maximum temperature differential of 100K was achieved. While maintaining hot heat sink temperature at ~285 K and the cold load temperature at ~265 K, a cooling power of 40W was measured. The second type regenerator system used ~0.215kg (0.108 kg Gd spheres and 0.107kg Gd0.74Tb0.26 spheres) in a layered configuration. Under similar operating conditions, a cooling power of 28W was measured. This showed that the layered design was able to provide ~70% of the cooling power with only ~22% of the magnetic material. In addition, 5 thermocouples were embedded along the central axis to measure the temperature distribution. The temperatures measured indicated that the axial temperature profile from hot to cold in the layered regenerator is non-linear. Finally, based upon these results an advanced MCHL design will be presented which has the potential to increase the FOM for hydrogen liquefaction from 0.35 of current Claude-cycle based liquefiers to 0.5 or more.
5:15 PM - *EE11.1.06
Caloric, Meet Regenerator: You Have a Volume Problem
Andrew Rowe 1,Theo Christiaanse 1,Premakumara Govindapa 1,Iman Niknia 1,Reed Teyber 1,Paulo Trevizoli 1
1 Univ of Victoria Victoria Canada,Show Abstract
Caloric materials can be defined as those that exhibit reversible ordering due to changes in one of more generalized forces. The limited width of the ordering process as a function of temperature can be overcome by cascading layers of different materials as is found in an active regenerator. An active magnetic regenerator cycle (AMR) is a well-established process for extending the operating range of materials that exhibit a magnetic work mode. The abstraction of the AMR cycle to a more general active caloric regenerator (ACR) cycle is relatively straightforward and, in doing so, general requirements for any ACR process to achieve high heat pumping power and efficiency can be identified. Here, we identify the common parameters governing ACR performance, how these parameters are related to material properties, and how entropy is associated with both efficiency and cost.
Nini Pryds, Technical University of Denmark
Asaya Fujita, National Institute of Advanced Industrial Science and Technology (AIST Chubu)
Neil Mathur, University of Cambridge
Ichiro Takeuchi, University of Maryland
EE11.2: Session II
Wednesday AM, March 30, 2016
PCC North, 100 Level, Room 127 A
9:45 AM - *EE11.2.01
Electronic Phase Change and Entropic Functions in Transition Metal Oxides
Hidenori Takagi 3
1 Max Planck Institute for Solid State Research Stuttgart Germany,2 Department of Physics University of Tokyo Tokyo Japan,3 FMQ University of Stuttgart Stuttgart Germany,Show Abstract
The electric and magnetic properties of transition metal oxides (TMO) are in many casesoften dominated by electrons in d-orbitals. Large Coulomb repulsion between electrons accommodated in the spatially constrained d-orbitals tends to block the motion of electrons from one atom to another, atom and the electrons are highly entangled. Just like interacting atoms and molecules, the entangled electrons, called correlated electrons, form solid (insulator), and liquid (metal), and superfluid (superconductor) states inside the solid. The presence of the three degrees of freedom attached to electrons – , charge, spin and orbital, enrich these electronic phases further. These rich electronic phases are competeing with each other ion a delicate balance. Even a minute perturbation can often causeinduce a phase change, giving rise to a gigantic dramatic response to external fields. Those areis is the hallmarks of phase change functions in transition metal oxides, including useful as sensors, memoriesy and for signal conversion .
In this talk, we would like to discuss the application of phase change concept to entropic functions rather than the long discussed functions mentioned above. Partly because of the multiple degrees of freedom, the complicated electronic phases in transition metal oxides are often highly entropic. The high entropy can manifest itself in a large entropy (enthalpy) change associated with the electronic phase change. VO2 is known to show a paramagnetic metal (liquid) to a nonmagnetic insulator (solid) transition around room temperature, where we indeed observed a large entropy change per volume, comparable to that of water-ice transition. This can be utilized as a "solid" electronic ice pack of which melting temperature is "tunable" upon doping. We can construct electronic icepack working at 10 C, which for example may be used to preserve human tissues during surgery. The large electric entropy coupled with electric current can be utilized for thermoelectric conversion. The oxide thermoelectrics, NaxCoO2, can be viewed as a realization of such scenario. Other possible application of the large electronic entropy will be discussed.
 H.Takagi and H.Y.Hwang, Science 327 (2010) 1601.
10:15 AM - EE11.2.02
Non-Universal Scaling of the Magnetocaloric Effect as an Insight into Magnetic Phase Transitions
Anders Smith 1,Kaspar Nielsen 1,Henrique Bez 1,Christian Bahl 1
1 Department of Energy Conversion and Storage Technical University of Denmark Roskilde Denmark,Show Abstract
Recently we showed theoretically that the field dependence of the magnetocaloric quantities (isothermal entropy change, ΔS, and adiabatic temperature change, ΔTad) close to a ferromagnetic-to-paramagnetic phase transition is not uniquely determined by the critical exponents of the transition. Here we show that this non-universality of the magnetocaloric effect is observable experimentally, and that it can be used to gain insight into the properties of the phase transition and the magnitude of the spin-lattice interactions. We measure the field dependence of the isothermal entropy change of the manganite series La0.67Ca0.33−xSrxMnO3 directly by using calorimetry in a custom-built differential scanning calorimeter equipped with a permanent magnet array which can produce a variable magnetic field. For the series of second order materials 0.0375 < x < 0.0750 we find that the scaling exponent characterizing the field dependence of ΔS near Tc decreases monotonously from 0.7 to 0.6 as x decreases from 0.0750 to 0.0375, showing non-universal behaviour. The results can be interpreted using a mean-field approach in which the exchange coupling depends linearly on the spin-spin distance. This so-called Bean-Rodbell model has been used extensively to model magnetocaloric materials with a first order phase transition. However, as we show, it can also give important insight into second order phase transitions. By fitting the full field dependence using the Bean-Rodbell model we can extract both the strength of the spin-lattice interaction and the spread in Tc due to compositional variations within the samples. The former increases as x decreases, giving rise to increasingly first-order-like behaviour. We find that all samples with 0.0375 < x < 0.0750 are second order. The same approach applied to a sample with x = 0 identifies this compound as (weakly) first order. Thus a careful determination of the field dependence of the isothermal entropy change close to the transition temperature not only allows us to determine the variation of the effective spin-lattice coupling as a function of the strontium content of La0.67Ca0.33−xSrxMnO3, but also gives information on the order of the phase transition.
 A. Smith, K.K. Nielsen and C.R.H. Bahl, Phys. Rev. B 90 (2014) 104422.
 A. Smith, K.K. Nielsen, H.N. Bez, and C.R.H. Bahl, submitted to Phys. Rev. B (2015).
10:30 AM - *EE11.2.03
Element-Resolved Thermodynamics of the Conventional Magnetocaloric System La-Fe-Si
Markus Gruner 2,Werner Keune 1,Beatrice Roldan Cuenya 3,Claudia Weis 1,Joachim Landers 1,Sergey Makarov 1,David Klar 1,Soma Salamon 1,Michael Hu 4,Esen Alp 4,Jiyong Zhao 4,Maria Krautz 5,Oliver Gutfleisch 6,Heiko Wende 1
1 Faculty of Physics University of Duisburg-Essen Duisburg Germany,2 Forschungsneutronenquelle FRM-II Technical University Munich Garching Germany,1 Faculty of Physics University of Duisburg-Essen Duisburg Germany3 Department of Physics Ruhr-University Bochum Bochum Germany4 Advanced Photon Source Argonne National Laboratory Argonne United States5 IFW Dresden Dresden Germany6 Materials Science TU Darmstadt Darmstadt GermanyShow Abstract
Fe13-xSix – based systems (1.0 ≤ x ≤ 1.6), which crystallize in the NaZn13 structure, are in their hydrogenated form one of the most promising systems for magnetic refrigeration applications.
They undergo a first-order magnetic transition with a narrow hysteresis providing large adiabatic temperature and isothermal entropy changes in an external magnetic field. The isothermal entropy change ΔSiso across TC is usually divided up as ΔSiso = ΔSmag + ΔSlat + ΔSel, assuming independent contributions from the magnetic, lattice (vibrational) and electronic degrees of freedom, respectively.
We combine two independent approaches, first-principles calculations in the framework of
density functional theory and nuclear resonant inelastic X-ray scattering, in order to compare lattice dynamics in both, the ferromagnetic and the paramagnetic phase, and thus ΔSlat, resolving the contributions of the elemental constituents.
Our results demonstrate an unusual and significant effect of the magnetic phase transition on the
element-resolved vibrational density of states of La-Fe-Si. This involves the disappearance of a high-energy peak in connection with an overall softening of phonons in the paramagnetic phase. The consequence is a significant increase in ΔSlat near TC, which contributes cooperatively with ΔSmag and ΔSel to the good magneto- and barocaloric properties. This is unexpected, since conventional Grüneisen theory predicts a negative ΔSlat according to the large volume decrease at the transition.
Instead, we observe an anomalous magneto-elastic softening which is solely associated with the Fe-subsystem. It originates from adiabatic electron-phonon coupling caused by specific changes in the electronic density of states at the Fermi level arising from the itinerant electron metamagnetism of Fe and implies a substantial interdependece of all relevant degrees of freedom.
Financial support from the Deutsche Forschungsgemeinschaft through SPP1599 and SFB/TRR80 is gratefully acknowledged.
11:30 AM - *EE11.2.04
In Situ XRD and 3D Imaging Techniques for the Study of Magnetocaloric Materials
Anja Waske 1,Alexander Funk 2,Bruno Weise 2,Marius Bierdel 2,Alexander Rack 3
1 IFW Dresden Dresden Germany,1 IFW Dresden Dresden Germany,2 TU Dresden Dresden Germany3 ESRF Grenoble FranceShow Abstract
First-order transitions in magnetocaloric materials are the source of strong changes in their magnetization and entropy, giving rise to large magnetocaloric effects. These kind of transitions show interesting phenomena, like phase coexistence and thermal arrest. The way each phase nucleates from the other phase is largely unknown at a microscopic level, besides this being important not only from a fundamental point of view, but also for technical aspects like choosing the geometry of the sample or identifying an upper limit for the cycling frequency.
In La(Fe,Si)13, an isostructural first-order transition occurs at the critical temperature TC, which retains the structural symmetry of the crystal but leads to an abrupt increase in the lattice parameter. We use in-situ computed tomography and situ X-ray diffraction on magnetocaloric La(Fe,Si)13 to study the magnetovolume transition as a function of temperature. The experiments have been carried out at the beamline ID 19 at the ESRF in Grenoble (tomography) and the Petra III /2.1 beamline at DESY in Hamburg (XRD), respectively. A stream of cold nitrogen gas was used to drive the magnetocaloric material through the phase transition upon cooling. Using these methods, we show that i) by 3D imaging it is possible to track the magnetovolume transition, ii) nucleation and growth of the ferromagnetic phase depends strongly on surface morphology and iii) the virgin effect in magnetocaloric La(Fe,Si)13 is connected to the formation of cracks. These findings connect microstructural aspects of the first-order transition to important properties like hysteresis and kinetics of the phase transition and can therefore help to tailor magnetocaloric materials towards application.
12:00 PM - EE11.2.05
Entropic Features of Paramagnetic State in Some Itinerant Electron-Type Caloric Compounds
Asaya Fujita 1,Kozuhiro Minakuchi 1
1 AIST Chubu Aichi Japan,Show Abstract
In a phase transition, a change in the internal energy is compensated by the entropiy change, in contrast to a ideal-gas packed cylinder where a change in the internal energy is induced by the work of piston. Especially in the first-order phase transition, an distinct change in entropy causes a latent heat. Desorption/absorption of the latent heat is therefore not equivalent to external work that triggers the phase transition. Difference between input and output (external trigger and the emerged heat amount) governs a figure of merit in cooling functions by using the first order transition.
Recently, various giant caloric phenomena have been reported 1). We also found some examples such as a giant magnetocaloric effect in La(Fe,Si)13 2), barocaloric one in Mn3GaN 3) and electrocaloric one in VO2 3) Among them, important factors for enhancement of caloric effect are: magnitude of entropy in the normal (disordered) state in addition to that in the ordered state and a cross correlation of plural degrees of freedom in the “entropy carrier” such as spin, charge, orbital or lattice vibration. In this presentation, we focus on the paramagnetic state in the viewpoint of entropic contributions.
First-principles calculation allows us to investigate the disordered local moment (DLM) state, which is realized by adiabatically randomized dispersion of the principle axis for local moment 5). We carried out this calculation for La(Fe,Si)13 case by adopting a compensated (an Ising - like) DLM arrangement. Resultant value of amplitude of DLM is about 1.8 μB for Fe II site. A density of state at the Fermi energy for the DLM state has almost same magnitude as that in a non-magnetic (NM) state. This means that the difference of the electronic entropy part is not so large between the NM and DLM paramagnets, while the fluctuation of DLM generates a large entropic contribution in which a maximum of R ln(2J+1) (where R is the gas constant and J corresponds to effective magnetic carrier of DLM ). In experiments, the existence of the DLM is detected by the anomalous Hall effect measurement. Temperature dependence of electrical resistivity also clearly suggests a strong influence of the DLM fluctuations. We also found a characteristic feature of DLM under a structural frustration in the antiperovskite-type Mn3XN compounds.
1) Moya et al., Nature Mater. 13, 439 (2014)
2) Fujita et al., Phys. Rev. B 67, 104416 (2003)
3) Matsunami et al., Nature Mater. 14, 73 (2015)
4) Matsunami and Fujita, Appl. Phys. Lett. 106, 042901 (2015).
5) Staunton et al., J. Phys.: Condens. Matter, 26, 274210 (2014)
12:15 PM - EE11.2.06
La(Fe,Mn,Si)13Hz First Order Phase Transition Evaluated by XRD Methods
Henrique Bez 1,Kaspar Nielsen 1,Anders Smith 1,Christian Bahl 1
1 DTU Roskilde Denmark,Show Abstract
First order magnetic phase transition materials present a large magnetocaloric effect around the transition. Also, these materials usually undergo a large volume change around the transition. This may lead to some challenges for applications, as they may break apart during the field changes, due to high internal stresses. A promising magnetocaloric material with first order phase transition is La(Fe,Mn,Si)13Hz, of which the transition temperature can be controlled by the Mn amount. In this work we use the powder x-ray diffraction (XRD) method to evaluate the temperature dependence of the crystalline properties during the transition as a function of Mn content. We evaluate three different compositions of LaFe13-x-yMnxSiyH1.65 with first order phase transition, x=0.25, 0.22 and 0.06; y=1.28, 1.23 and 1.18. The XRD patterns were refined using the Rietveld method. The Curie temperature, TC, increased with the decrease of x. Furthermore, rather than having a discontinuous volume change, both phases paramagnetic (with smaller volume) and ferromagnetic (with larger volume) were observed as peak overlaps in the patterns around the TC. This effect is related to stoichiometrical inhomogeneity. Supplementary magnetization measurements suggests that this behaviour is also related to the fact that finely ground particles have more freedom to expand/contract, so they are not constricted by surrounding grains, which would lead to sharp transitions, as observed on e.g. sintered parts. Moreover the absolute volume change from the ferromagnetic to paramagnetic phase increases with the decrease of x. We then use the Williamson-Hall method  to calculate strain effects on the crystallites during the transition. This method assumes that strains in the crystallites may shift the XRD pattern peaks (uniform strain) or broaden the peaks (non-uniform strain). In this method, the strain may be calculated by the following equation: βcos(θ) = C +4εsin(θ), where theta is the peaks’ reflection angle θ, β is the full width half maximum of the respective peaks, C is a constant and ε is the strain. We observed the evolution of the strain in the ferromagnetic phase as the transition occurs. It has been observed that multi-grain particles form cracks during the transition due to the stress generated by this strain . The evidence of these strains is crucial for the design of a material which avoids fracture during the transition.
 G.K. Williamson and W. H. Hall, Acta Metall. 1, 22-31 (1953)
 Waske et al. Phys. Status Solidi RRL, 1–5 (2015).
12:30 PM - EE11.2.07
First Principles Modeling of Magnetostructural Transformations and Magnetocaloric Effect
Durga Paudyal 1,Vitalij Pecharsky 2,Karl Gschneidner 2
1 Ames Laboratory, Iowa State University Ames United States,1 Ames Laboratory, Iowa State University Ames United States,2 Department of Materials Science and Engineering, Iowa State University Ames United StatesShow Abstract
Density functional theory (DFT) calculations describe ground state properties. The direct evaluation of magnetic entropy change from these calculations is still not possible. A possible pathway to evaluate magnetic entropy change is to couple DFT results with magneto-thermodynamic models. The calculated magnetic moments from DFT and Curie temperatures from coupled DFT plus Heisenberg model can be employed as inputs to magneto-thermodynamic models, e.g. Brillouin function, free energy, and entropy and solved self consistently to evaluate magnetostructural transition temperature and corresponding magnetic entropy change. Here we discuss this pathway using HoCo2 system as an example, which has both first order magnetostructural and second order structural transformations.
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The research was performed at the Ames Laboratory, which is operated for the U.S. DOE by Iowa State University under contract # DE-AC02-07CH11358.
EE11.3: Session III
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 127 A
2:30 PM - *EE11.3.01
DRREAM: Drastically Reduced Use of Rare Earths in Applications of Magnetocalorics
Lesley Cohen 1,Karl Sandeman 2
1 Imperial College London United Kingdom,1 Imperial College London United Kingdom,2 Brooklyn College New York United StatesShow Abstract
The aim of DRREAM, an EC-FP7-funded collaborative research project , has been to reduce the use of rare earths (REs) in the life cycle of a future magnetic cooling device. We forecast that the most significant reduction in the required volume of RE-containing permanent magnet will come from the use of refrigerants with enhanced magnetocaloric effects and from the improved heat transfer properties of optimally-produced regenerator parts. Efforts in these directions, and in the minimisation of wastage in the production of regenerator parts, will be described.
The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 310748.
Key Words: Magnetic cooling, Magnetic phase transition, Net shape manufacturing.
3:00 PM - EE11.3.02
Exploring Magnetic Frustration in Antiperovskite Mn Nitrides
David Boldrin 1,Oliver Baumfeld 1,Zsolt Gercsi 2,Jan Zemen 1,Lesley Cohen 1,Karl Sandeman 3
1 Department of Physics Imperial College London London United Kingdom,1 Department of Physics Imperial College London London United Kingdom,2 CRANN Trinity College Dublin Dublin Ireland1 Department of Physics Imperial College London London United Kingdom,3 Department of Physics Brooklyn College New York United StatesShow Abstract
The family of antiperovskite manganese nitrides, Mn4-xTxN (T = Sn,Ni,Zn,Ga...), have recently attracted much attention due to the various functional properties these materials display, such as baro- and magnetocaloric effects, negative thermal expansion and piezomagnetism. The underlying mechanism behind these is closely linked to the non-collinear antiferromagnetic structure and the strong magneto-structural coupling of this with the cubic lattice. For the majority of x=1 members the antiferromagnetic structure, and the transition from paramagnetism, has been well documented. However, for x < 1 an additional ferromagnetic component appears that further frustrates the magnetism. Particularly for T = Sn and Ni, the magnetic structure for this series has not been thoroughly explored since preliminary magnetisation and neutron diffraction experiments over 30 years ago. These experiments built a phase diagram with distinct ferromagnetic and antiferromagnetic regions, with clear transitions between the two. Here we show bulk magnetisation and heat capacity data on Mn4-xNixN and Mn4-xSnxN that conflict with this relatively simple picture. Our results are compatible with a coexistence of both antiferro- and ferromagnetism as x is lowered, which is significant as it means the crucial non-collinear antiferromagnetic structure is preserved, in opposition to previous understanding. Moreover, we find a peculiar negative magnetisation that may be related to coupling between the two magnetic phases. The complex competing interactions in these materials may lead to enhanced properties found in the x=1 members, whilst manipulation of x allows optimisation of these properties near room temperature.
The authors acknowledge funding from “Develpoment of advanced magnetic materials without or with reduced used of critical raw materials (DREEAM) EC FP7 Grant Agreement no:310748"
3:15 PM - EE11.3.03
Cooperative Lattice Distortions in the Magnetostructural Compound AlFe2B2 with Magnetocaloric Potential
Laura Lewis 1,Brian Lejeune 1,Radhika Barua 1,Enric Stern-Taulats 2,Lluis Manosa 2,Antoni Planes 2
1 Northeastern Univ Boston United States,2 Universitat de Barcelona Barcelona SpainShow Abstract
Understanding correlations between the magnetic response and the crystal structure in the vicinity of the magnetostructural transition is key to tailoring the response of materials with magnetocaloric potential. In particular, the ferromagnetic AlFe2B2 compound with the layered AlMn2B2-type structure is reported to exhibit a magnetic transition of relevance for magnetocaloric cooling. Results derived from magnetic, structural and calorimetric probes confirm a thermodynamically first-order magnetic phase change in the vicinity of the AlFe2B2 Curie temperature of ~ 300 K. Analysis of lattice parameter trends through the phase transition reveals cooperative distortions in the (ac) plane layers and along the orthorhombic b-axis that compensate to produce a conserved unit cell volume and a very small volumetric thermal expansion coefficient with a magnitude smaller than that of Al in the same temperature range. These results will be presented within a fundamental electronic phase transition perspective as well as within an applied technological context.
Research was funded in part by Northeastern University and by the US Army under grant W911NF-10-2-0098, subaward 15-215456-03-00.
3:30 PM - EE11.3.04
Some Aspects of Magnetocaloric and Elastocaloric Behavior of Metamagnetic Shape Memory Alloys
Volodymyr Chernenko 2,Christian Aguilar-Ortiz 3,Pablo Alvarez-Alonso 4,Elena Villa 5,Horacio Flores-Zuniga 3
1 BCMaterials amp; University of Basque Country Bilbao Spain,2 Ikerbasque, Basque Foundation for Science Bilbao Spain,3 División de Materiales Avanzados, Instituto Potosino de Investigación Científica y Tecnológica A.C. San Luis Potosí Mexico4 Electricidad y Electrónica, Universidad del País Vasco (UPV/EHU) Leioa Spain5 CNR IENI Unità di Lecco, Lecco Lecco SpainShow Abstract
Alongside the development of magnetocaloric materials exhibiting a large magnetic field induced entropy change in the vicinity of the second order magnetic transitions, the enormous efforts have been made last decade in advancement of the materials undergoing the first order magnetostructural transformations as an origin of the so-called giant magnetocaloric effect (GMCE). Among the latter materials, the so-called metamagnetic shape memory alloys (MetaMSMAs), such as the Mn-rich off-stoichiometric Ni2Mn(Ga,In,Sn,Sb) Heusler alloys, exhibiting a magnetostructural transformation from the ferromagnetic austenite into weakly magnetic martensite, are of a special interest because they are cost-effective, rare-earth-element free and nontoxic, as well as allow the easy-tunable parameters of GMCE.
The following aspects of transformation behavior, GMCE and elastocaloric effect of MetaMSMAs will be considered.
(i) Influence of Fe doping and magnetic field on the magnetic contribution to the total entropy change at the martensitic transformation in Ni50-xFexMn40Sn10 (x = 0, 2, 4, 6, 8 at.%) melt-spun ribbons.
(ii) The role of the transformation volume change in the magnetocaloric effect.
(iii) Landau type thermodynamics of GMCE in MetaMSMAs.
(iv) Underlying physics of the experimentally found inverse elastocaloric effect in the MetaMSMAs ribbons.
4:15 PM - *EE11.3.05
Electrocaloric Cooling-Present Advances and Future Perspectives
Qiming Zhang 1
1 Pennsylvania State Univ University Park United States,Show Abstract
Electrocaloric effect (ECE) is the ability of a dielectric to change its temperature and entropy as an electric field is applied and released. It provides an effective means to realize solid-state cooling devices that are environmentally benign and potentially highly energy efficient. In this talk I will present the recent breakthroughs in electrocaloric materials, including these exhibiting giant electrocaloric effect, where an adiabatic temperature change DT > 40 oC has been obtained in several nano-structured ferroelectrics. EC cooling devices based on these new materials, as well as challenges and future perspectives will be discussed.
4:45 PM - EE11.3.06
Calorimetric Studies of Electrocaloric Polymeric Films: Creating Material Requirements from Sub-Component Level Studies
Joseph Mantese 1,Subramanyaravi Annapragada 1,Wei Xie 1,John Miano 1,Thomas Radcliff 1,William Rioux 1,Parmesh Verma 1
1 United Technologies Res Ctr East Hartford United States,Show Abstract
The temperature lift and thermal capacity of thin film, PVDF-based, electrocaloric materials were studied using vacuum based micro-calorimetry capable of discerning temperature variations of
5:00 PM - EE11.3.07
Electrocaloric Heat Pump Design and Optimization
David Schwartz 1,Sylvia Smullin 1,Yunda Wang 1
1 PARC Palo Alto United States,Show Abstract
Utilization of electrocaloric materials in a heat pump requires a system design that can efficiently transfer heat to and from an electrocaloric element. One promising design topology uses heat switches, elements with a controllable thermal conductance. We will present analytical and numerical models of a heat-switch-based system that incorporate detailed parameters of electrocaloric materials and capacitors, heat switches, and cycle operation. We will show that system optimization depends on the combined thermal properties of all system elements as well as operating conditions. We will also describe practical figures of merit provided by the models for prediction of system performance. The numerical model is validated with experimental data and used to extrapolate to larger cooling systems.
5:15 PM - *EE11.3.08
Efficiency in Solid-State Cooling: Can Electrocaloric Materials Make a Difference
Emmanuel Defay 1
1 Materials Science and Technology Luxembourg Institute of Science and Technology Belvaux Luxembourg,Show Abstract
Voltage-driven thermal changes known as electrocaloric (EC) effects are large in ferroelectric thin films near the Curie temperature, where entropic electrical phase transitions may be reversibly driven by electric fields DE that approach the high breakdown fields generically associated with thin films. The thermal changes in a single film are small, but macroscopic assemblies of ferroelectric films in the multilayer capacitor geometry have been proposed for cheap, environmentally friendly and energy efficient cooling applications. However, candidate EC materials have hitherto only been analysed in terms of EC performance, i.e. the change in isothermal entropy DS, the isothermal heat Q, and the change in adiabatic temperature DT. Surprisingly, the corresponding electrical work W that is done when charging and discharging the host EC capacitors has been neglected. Therefore we introduce here electrocaloric efficiency h to describe the ratio of reversible electrocaloric heat to reversible electrical work under isothermal conditions. This figure of merit permits a comparison of EC materials that does not depend on details of any refrigeration cycle, i.e. the type of cycle, the hot and cold temperatures of the EC material, and the sink and load temperatures. We also introduce a way to substantially improve the overall efficiency of EC coolers through the use of simple electronic components. Optimal cycles are then compared with other existing cycles, namely vapour-compression (standard fridges), magnetocaloric and elastocaloric. This analysis should in future guide the selection of electrocaloric, elastocaloric and magnetocaloric materials for novel cooling devices that are energy efficient.
EE11.4: Poster Session
Wednesday PM, March 30, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - EE11.4.01
Magnetocaloric and Transport Properties of Off-Stoichiometric GdNi2Mnx
Anil Aryal 1,Abdiel Quetz 1,Sudip Pandey 1,Tapas Samanta 2,Igor Dubenko 1,Shane Stadler 2,Naushad Ali 1
1 Southern Illinois Univ Carbondale United States,2 Louisiana State University Baton Rouge United StatesShow Abstract
The Magnetic and Magnetocaloric effects (MCE), electrical resistivity ρ(T), and magnetoresistance (MR) of the rare-earth intermetallic compounds GdNi2Mnx (x = 0.5 ,0.8, 1.2, 1.4, and 1.5) have been studied using magnetization and resistivity measurements. The maximum value of magnetic entropy changes (-ΔSM) near TC for ΔH = 5T was found to be 3.1 J/KgK, 2.8 J/KgK, 2.9 J/KgK, and 2.5 J/Kg K for x = 0.8, 1.2, 1.4, and 1.5 respectively. The contribution to electrical resistivity ρ(T) from electron–phonon interactions (ρph(T)) and magnetic scattering (ρmag(T)) and the residual resistivity ρo in these compounds have been determined. At high temperature the compounds show a slowly increasing in ρ(T) curve. In the temperature interval T >>TC, ρmag(T) is considered to be temperature independent and the changes in the total resistivity are due ρph(T). Below TC, ρmag(T) undergoes a sharp, continuous decrease that dominated over the linear decrease in ρph(T). This results in the overall decrease in total ρ(T) below TC. At low temperature, ρ(T) follows a T2 law according to ρ(T) = ρo+AT2, which suggests a dominant electron–electron scattering behavior. The value of constant was found to be about A=3.2 nΩcm/K2. The residual resistivity (ρo) in these compounds was calculated to be 0.19 mΩ cm and, 0.06 mΩ cm for x = 0.5 and 1.5, respectively. Using Matthiessen’s rule, which states that ρ(T) = ρo+ ρph(T)+ρmag(T), the ρmag (constant) contribution to the total resistivity in these compounds were calculated as 0.02 mΩ cm, 0.15 mΩ cm for x =0.5 and x=1.5 respectively, by extrapolation of ρ(T) to T=0 from the high temperature region (T >200K). The maximum value of the MR in H=5T was found to be ~ -1.1% for x = 0.5 near TC, and -7 % for x=1.5 near T =80K.
Acknowledgements: This work was supported by the U.S. Department of Energy (DOE), Office of Science, BasicEnergy Sciences (BES) under Award No. DE-FG02-06ER46291and DE-FG02-13ER46946.
9:00 PM - EE11.4.02
Large Room Temperature Magnetocaloric Effect with Low Thermal Hysteresis in Polycrystalline Ni50Mn34In14Ga2 Alloy
Juan Camarillo 1,Horacio Flores-Zuniga 1,David Rios-Jara 1,Jose Luis Sanchez Llamazares 1,Enric Stern-Taulats 2,Antoni Planes 2,Lluis Manosa 2
1 Instituto Potosino de Investigación Científica y Tecnológica A. C. San Luis Potosi Mexico,2 Estructura i Constituents de la materia Universitat de Barcelona Barcelona SpainShow Abstract
We have determined the magnetic entropy change and relative cooling power across the first order martensitic transformation for a polycrystalline bulk Heusler alloy of nominal composition Ni50Mn34In14Ga2 (Ni50.4Mn34.2In13.3Ga2.1 determined by EDS). The sample was prepared by arc-melting the pure elements under an argon atmosphere in water-cooled Cu crucible; it was re-melted several times to ensure a good starting homogeneity. It was annealed at 1173 K during 24 h in sealed quartz ampoule under Ar atmosphere and quenched into ice-water followed annealed. The room temperature XRD pattern shows an austenite with L21 structure. From DSC measurements the enthalpy and entropy of transformation were determined as 7.3 Jg-1 and 26.2 Jkg-1K-1, respectively. The alloy exhibits martensitic transformation at TM= 280 K and low thermal hysteresis of 5 K. Magnetic entropy change as a function of temperature ΔSM(T) curves were determined up to a magnetic field change of 5 T from both DSC as a function of applied magnetic field measurements using a purpose-built calorimeter , and via the application of the Maxwell relation. The results obtained from both methods are in good agreement. For a field change of 5 T a maximum of magnetic entropy change ΔSMmax of 23.6 Jkg-1K-1 (23.0 Jkg-1K-1) was obtained from DSC(µoH) (magnetization) measurements. This value is about 3 times the one previously reported for an alloy with a similar composition ; ΔSMmax keeps over 20 Jkg-1K-1 from 272 to 281 K. From the DSC measurements under magnetic field it is shown that from 3 to 5 T the reversibility of the magnetocaloric effect was between 19 and 22 Jkg-1K-1. The sample shows a relative cooling power of 250 Jkg-1. After subtracting the average hysteresis loss an affective relative cooling power of 166 Jkg-1 was obtained. This is a 66% of the highest value reported for a Heusler alloy (Ni40Co10Mn40Sn10) .
 B. Emre et al., J. Appl. Phys. 113, 213905 (2013).
 S. Aksoy et al., Appl. Phys. Lett. 91, 241916 (2007).
 L. Huang et al., Appl. Phys. Lett. 104, 132407 (2014)
9:00 PM - EE11.4.04
Growth of Epitaxial BaTi1-xZrxO3 Thin-Films for Electrocaloric Studies
Stefan Engelhardt 3,Michael Mietschke 3,Oliver Mey 1,Paul Chekhonin 1,Sebastian Faehler 1,Christian Molin 2,Sylvia Gebhardt 2,Kornelius Nielsch 3,Ruben Huehne 1
1 Institute for Metallic Materials IFW Dresden Dresden Germany,3 Institute for Material Science TU Dresden Dresden Germany,1 Institute for Metallic Materials IFW Dresden Dresden Germany2 Department of Smart Materials and Systems Fraunhofer Institute for Ceramic Technologies and Systems Dresden GermanyShow Abstract
Materials, which show an electrocaloric effect, got a renewed interest due to the quest for energy-efficient cooling technologies. A change of temperature is induced in these materials by the application of an electric field close to a diffusionless phase transformation in particular near the ferroelectric Curie temperature. Our goal is to study the correlation between this electrocaloric effect and the microstructural changes at the phase transition in detail, which might enable to tune the materials for specific applications. Therefore, we have chosen BaTiO3-BaZrO3 as model system as the type of phase transition changes from a normal to relaxor ferroelectric behavior with increasing Zr content. Furthermore, we hope to facilitate the detailed microstructural analysis in these materials with the application of epitaxial films.
Therefore, epitaxial BaTi1-xZrxO3 films were grown by pulsed laser deposition on (001) as well as on (111) oriented single crystalline SrTiO3 substrates utilizing an additional conducting SrRuO3 buffer layer, which is used as bottom electrode for the ferroelectric characterization afterwards. The structural properties of the grown films were studied by high-resolution X-ray diffraction as well as scanning electron and atomic force microscopy. A detailed microstructural analysis was performed by transmission electron microscopy on selected samples. Depending on the growth parameters, a twin-free epitaxial growth and a smooth surface structure is observed. Finally, the dielectric properties of the grown films as the relative permittivity and the dielectric loss were determined in dependence of temperature. Simultaneously, temperature dependent ferroelectric polarization measurements allow estimating the electrocaloric behavior. In particular, we will discuss the influence of the Zr content and the substrate orientation on the functional properties of these films.
This work is supported by the DFG priority program 1599 “Ferroic cooling”.
9:00 PM - EE11.4.05
Giant Reversible Inverse Magnetocaloric Effect in Ni50Mn35In15 Heusler alloys
Abdiel Quetz 1,Yurii Koshkid'ko 3,Ivan Titov 4,Igor Rodionov 4,Sudip Pandey 1,Anil Aryal 1,Pablo Ibarra Gaytan 5,Valery Prudnikov 4,Alexander Granovsky 4,Igor Dubenko 1,Tapas Samanta 6,Jacek Cwik 2,Jose Luis Sanchez Llamazares 5,Shane Stadler 6,Erkki Lahderanta 7,Naushad Ali 1
1 Department of Physics Southern Illinois University Carbondale Carbondale United States,2 VSB Technical University of Ostrava Ostrava-Poruba Czech Republic,3 International Laboratory of High Magnetic Fields and Low Temperatures Wroclaw Poland4 Faculty of Physics Moscow State University Vorob’evy Gory Russian Federation5 Instituto Potosino de Investigación Cientifica y Tecnológica A.C. Camino a la Presa San Jose 2055, Col. Lomas 4a sección, San Luis Potosi Mexico6 Department of Physics amp; Astronomy Louisiana State University Baton Rouge United States2 VSB Technical University of Ostrava Ostrava-Poruba Czech Republic7 University of Technology Lappeenranta FinlandShow Abstract
The magnetic and magnetocaloric properties of the off-stoichiometric In-based Heusler alloy Ni50Mn35In15 have been studied in the vicinity of the phase transition temperatures using magnetization and direct adiabatic temperature change (ΔTad) measurements in magnetic fields up to 14 T.The magnetostructural phase transitions (MSTs) between a martensitic phase (MP) with low magnetization (paramagnetic or antiferromagnetic) and a nearly ferromagnetic austenitic phase were detected from thermomagnetic curves, M(T,H), at the applied magnetic fields up to 5 T. The MST temperature was found to be nearly independent of magnetic field for H
9:00 PM - EE11.4.05
Magnetocaloric Properties of Rapidly Solidified ErMn2 Alloy Ribbons
Jose Luis Sanchez Llamazares 1,Pablo Ibarra Gaytan 1,Cesar Fidel Sanchez-Valdes 2,Pablo Alvarez-Alonso 3,A.D. Martinez-Iniesta 4,J. A. Garcia-Carrillo 5
1 Instituto Potosino de Investigación Científica y Tecnológica A.C. San Luis Potosí, SLP Mexico,2 Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Ensenada Mexico3 Departamento de Electricidad y Electrónica Universidad del País Vasco (UPV/EHU) Bilbao Spain1 Instituto Potosino de Investigación Científica y Tecnológica A.C. San Luis Potosí, SLP Mexico,4 Universidad Tecnológica de Tula-Tepeji Tula de Allende Mexico1 Instituto Potosino de Investigación Científica y Tecnológica A.C. San Luis Potosí, SLP Mexico,5 Facultad de Ciencias Químicas Benemérita Universidad Autónoma de San Luis Potosí San Luis Potosí MexicoShow Abstract
The magnetocaloric (MC) properties of binary Laves phases based on rare earths (R) have been extensively investigated owing to their potential as magnetic refrigerants in the cryogenic temperature range. However, most studies have been focused mainly on RX2 compounds with X = Al, Ni and Co [1, 2]. Recently, Xuo et al. reported a large reversible MC effect in RMn2 compounds (R = Tb, Dy, Ho, and Er), highlighting their potential as working MC substances in the 10-80 K range. For bulk ErMn2 alloys produced after a prolonged thermal annealing (1073 K; 7 days), they found large values of the maximum magnetic entropy change ΔSMmax and refrigerant capacity RC (i.e., -25.5 (-13.4) Jkg-1K-1 and 316 (100) Jkg-1, respectively, for a field change of 5 (2) T). The present investigation was undertaken to produce rapidly solidified ribbons of this binary compound by using the melt-spinning technique as well as to study their MC properties. Ribbon samples were produced from bulk arc melted alloys previously obtained from highly pure elements (≥ 99.9 %). Rapid solidification processing was carried out in a highly pure Ar environment using an Edmund Bühler SC melt spinner system; ribbon flakes were obtained at a moderate wheel linear speed of 15 ms-1. The X-ray diffraction (XRD) analysis showed that the major phase formed crystallized into the MgZn2-type hexagonal structure (C14 type); however, both XRD and SEM analyses revealed the formation of impurity phases (i.e., Er6Mn23 and Er2O3). The M(T) curves, measured under 5 mT and 5 T, show that ErMn2 ribbons exhibit a saturation magnetization at 2 K of 138.1 Am2kg-1 and a Curie temperature of TC = 15 K. A field-induced metamagnetic transition at very low critical magnetic fields (0.1 T at 2 K) was observed (the Arrott plots method confirmed its first-order nature); this leads to a change of sign in the magnetic entropy change below 8 K and a low inverse MC effect (ΔSMmax = 2.5 Jkg-1K-1 at 2 K). For a magnetic field change of 5 T (2 T) applied along the ribbon length, the produced ribbons showed a peak value of the magnetic entropy change ΔSMmax of -21.1 (-11.4) Jkg-1K-1, a full-width at half-maximum δTFWHM for the ΔSM(T) curve of 20 (12) K, and RC = 408 (143) Jkg-1 (estimated from the product │ΔSMmax│× δTFWHM).
 N.A. de Oliveira and P. J. von Ranke, Rep. Prog. Rep. 489, 89 (2010)
 K.A. Gschneidner Jr., K. Pecharsky, and A.O. Tsokol, Rep. Prog. Phys. 68, 1479 (2005).
 Wenliang Zuo, Fengxia Hu, Jirong Sun, and Baogen Shen, J. Alloys Compd. 575, 162 (2013).
Nini Pryds, Technical University of Denmark
Asaya Fujita, National Institute of Advanced Industrial Science and Technology (AIST Chubu)
Neil Mathur, University of Cambridge
Ichiro Takeuchi, University of Maryland
EE11.5: Session IV
Thursday AM, March 31, 2016
PCC North, 100 Level, Room 127 A
9:30 AM - *EE11.5.01
Multicaloric Effects in First-Order Phase Transitions
Lluis Manosa 1
1 Universitat de Barcelona Barcelona Spain,Show Abstract
A caloric effect refers to the isothermal entropy or to the adiabatic temperature changes experienced by a material when subjected to the application of an external field. These effects are enhanced in the vicinity of a phase transition and to date several caloric effects have been reported (mangetocaloric, electrocaloric, barocaloric and elastocaloric) depending on the nature of the order parameter and of its conjugated external field [1,2].
Many caloric materials posses a strong coupling between different degrees of freedom, and they may also be sensitive to fields not conjugated to the order parameter. Such a cross-response opens-up the possibility of tuning the phase transition by a variety of external stimuli giving rise to a variety of caloric effects in a single material. A multicaloric effect refers to the case when more than one type of caloric effect is driven simultaneously or sequentially in a single sample .
In my talk I will report on recent experiments which provide experimental evidences for multicaloric effects in materials with first-order magnetostructural phase transitions.
Key Words: Multicaloric and caloric effects.
 L. Mañosa et al. J. Mater. Chem. A 1 (2013) 4925.
 X. Moya et al. Nature Mater. 13 (2014) 440.
10:00 AM - EE11.5.02
First Principles-Based Studies of the Electro-Caloric Effect in BaTiO3
Madhura Marathe 1,Anna Grünebohm 2,Claude Ederer 1
1 Materials Theory ETH Zurich Zurich Switzerland,2 Faculty of Physics and Center for Nanointegration, CENIDE University of Duisburg-Essen Duisburg GermanyShow Abstract
We use molecular dynamics simulations for a first principles-based effective Hamiltonian to study the electro-caloric (EC) effect in the prototypical ferroelectric material BaTiO3. We compare direct and indirect approaches to evaluate both the adiabatic EC temperature change as well as the isothermal EC entropy change, and we show that both approaches lead to identical results provided that the system does not actually undergo a first order phase transition . We also demonstrate that large EC response is obtained for electric fields beyond the critical field strength for the first order phase transition, and we estimate the latent heat contribution to the EC entropy change for cases where the system does indeed undergo a first order transition.
Furthermore, we analyze the dependence of the EC temperature change on the direction of the applied electric field in the vicinity of all three ferroelectric transitions in BaTiO3, and we discuss the possibility for observing an inverse EC effect (i.e. decreasing temperature under application of an electric field).
Finally, we study the effect of epitaxial strain on the EC effect in thin films of BaTiO3. We show that compressive strain leads to a strong increase of the EC temperature change and also of the temperature at which the maximal EC effect is observed . On the other hand, for tensile strain a multi-domain state is obtained over a large temperature interval around room temperature , which could extend the temperature range available for operating EC devices.
 M. Marathe et al., arXiv:1506.00525 (2015).
 M. Marathe and C. Ederer, Appl. Phys. Lett. 104, 212902 (2014).
 A. Grünebohm, M. Marathe, and C. Ederer, Appl. Phys. Lett. 107, 102901 (2015).
10:15 AM - EE11.5.03
Elastocaloric Performance of Low Fatigue TiNiCu-Based Thin-Films
Christoph Chluba 1,Hinnerk Ossmer 2,Manfred Kohl 2,Eckhard Quandt 1
1 Institute for Material Science University of Kiel Kiel Germany,2 Institute of Microstructure Technology Karlsruhe Institute of Technology Karlsruhe GermanyShow Abstract
Cooling devices based on the elastocaloric effect are promising candidates for the replacement of conventional vapor compression cooling which suffers from a high environmental impact and limited efficiency improvement possibilities. The elastocaloric effect describes a stress induced phase transformation that results in a temperature change of the material at adiabatic conditions. To use this effect in a continues cooling process, elastocaloric materials have to fulfill several requirements like high functional and structural fatigue resistance, adjustable transformation temperatures close to RT, high adiabatic temperature changes, a wide operational temperature range and a high coefficient of performance.
In this talk, the elastocaloric performance of Ti-rich TiNiCu-based thin films will be discussed. This compositions have the advantage of high functional stability of 10 million cycles which makes them very attractive for elastocaloric cooling applications (1). Cobalt and Iron addition is used to adjust the transformation temperature. The compositional influence on the elastocaloric parameters is investigated by temperature dependent tensile tests, infrared (IR) thermography and differential scanning calorimetry.
We found that the transformation temperatures can be easily adjusted from -50 °C to 60 °C by Cobalt and Iron content variation. Due to the small hysteresis of TiNiCu-based materials, the cooling efficiency is increased compared to sputtered binary NiTi films despite of a lower adiabatic temperature change of ~10 K measured by IR thermography. The operational temperature range of the single compositions is limited to ~50 K caused by a large Clausius-Clapeyron coefficient of 10 MPa/K. The transformation strain with 1-2 % is much smaller compared to binary NiTi which makes the mechanical loading of the material easier since the required actuator stroke is decreased. In summary, the good elastcaloric performance of Ti-rich TiNiCu-based compositions, combined with their high functional stability makes them promising materials for elastocaloric cooling applications.
(1) Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M.: Ultralow-fatigue shape memory alloy films, Science, 348 (2015), 1004-1007.
10:30 AM - *EE11.5.04
Materials Fatigue for Elastocaloric Cooling
Jun Cui 3,David Catalini 3,Naila Al Hasan 4,Michael Dahl 3,Ichiro Takeuchi 4
1 Iowa State University Ames United States,2 Materials Science and Engineering Ames Laboratory Ames United States,3 Energy and Environment Directorate Pacific Northwest National Laboratory Richland United States,3 Energy and Environment Directorate Pacific Northwest National Laboratory Richland United States4 Materials Science and Engineering University of Maryland College Park United StatesShow Abstract
Elastoclaoric cooling has demonstrated high efficiency (~80% Carnot) and minimum environmental impact. The physical principle of the thermoelastic cooling is based on stress induced structural phase transformation, whose latent is thermodynamically manipulated to achieve refrigeration. Unfortunately, the requirement of millions of cycles of large deformation is difficult to meet for most of the materials exhibiting elastoclaoric effect, making it difficult for the technology to be deployed for real world application. Efforts have been made to improve the fatigue properties of the most popular elastocaloric material, NiTi based shape memory alloy. In this talk, we discuss both the material approach and engineering approach. The material approach focuses on the inherent fatigue property, which is related to inclusion and void, and to the phase transformation compatibility. The engineering approach focuses on how the material is properly used. For example, while larger stress significantly reduce materials fatigue life, it does not necessarily bring out more cooling power from the material. There exists a stress optimum for cooling power and fatigue life. For another example, compressive stress may heal microcracks therefore a material under repeated compression stress may survive much longer than it is under tensile stress. In this talk, we discuss both approaches with specific examples, and report the results of three long-term fatigue tests of a bundled NiTi tubes under compressive stress.
11:30 AM - *EE11.5.05
Functional Fatigue of Elastocaloric NiTiCu-Based Thin-Films
Eckhard Quandt 1,Christoph Chluba 1,Wenwei Ge 2,Rodrigo Lima de Miranda 1,Julian Strobel 1,Lorenz Kienle 1,Manfred Wuttig 2
1 University of Kiel, Faculty of Engineering Kiel Germany,2 Department of Materials Science and Engineering University of Maryland Maryland United StatesShow Abstract
Caloric materials have the potential to serve as an environmentally friendly and more efficient alternative substitute in conventional vapor compression cooling. The principle of ferroic cooling is based on a solid state phase transformation initiated by an external field, in the case of elastocalorics by an external stress field. Combined with thin film processes this technology enables the development of small scale cooling devices required for mobile applications. Up to now, the major obstacle for the implementation of elastocaloric materials in cooling devices are the functional degradation and structural failure of the material. To investigate the underlying microstructural mechanisms TEM and synchrotron analyses of NiTiCu- based thin films are conducted in the pristine state and after superelastic cycling. A strong difference of superelastic degradation for Ti-rich compositions compared to near equiatomic compositions is found. While near equiatomic compositions already degrade severely during the first cycles, Ti-rich compositions are functionally stable for 107 full superelastic cycles (1). Using stress dependent in situ synchrotron investigations the change of lattice constants of B2 phase and stress induced B19 phase during the superelastic transformation can be quantified. This measurement enables the compatibility calculation of austenite and martensite phases which is known to have a strong influence on the superelastic hysteresis and the thermally induced transformation stability. The microstructural influences of grain size, precipitates and crystallographic compatibility on the functional degradation of NiTiCu-based thin films will be discussed.
(1) Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M.: Ultralow-fatigue shape memory alloy films, Science, 348 (2015), 1004-1007.
12:00 PM - EE11.5.06
Elastocaloric Micro Heat Pumping
Hinnerk Ossmer 1,Shuichi Miyazaki 2,Manfred Kohl 1
1 Karlsruhe Institute of Technology Eggenstein-Leopoldsh Germany,2 University of Tsukuba Tsukuba JapanShow Abstract
This paper presents an investigation of local strain and temperature profiles of cold-rolled TiNi-based foil specimens of 30 µm thickness and the corresponding development of a first demonstrator for elastocaloric micro heat pumping. The underlying elastocaloric effect is based on a diffusionless first order phase transformation between austenite (A) and martensite (M). In pseudoelastic shape memory alloys (SMAs), the phase transformation is induced by applying uniaxial stress. At present, demonstrators for elastocaloric cooling make use of bulk materials. However, using SMAs with high aspect ratio like SMA foils significantly improves heat transfer times. Targeted applications on small scales comprise temperature control of lab-on-chips, cooling in medical surgery and microelectronics.
Main challenges are size of elastocaloric effect, fatigue resistance and device design. Bridge samples are fabricated from textured Ti49.1Ni50.5Fe0.4 foils produced by cold rolling with a final cold rolling reduction of 40%. Rolling-induced texture reduces the critical stress for martensite transformation in rolling direction due to favorable orientation of grains. Cyclic tests up to 100 operation cycles demonstrate stabilization and reversible operation after about 10 cycles, which is attributed to the rolling induced texture. Tensile tests in the adiabatic limit show a self-heating /cooling of 20/-16 K due to stress-induced phase transformation.
A novel heat pumping design is developed consisting of pseudoelastic SMA bridges of 20 x 2 mm2 size that are fixed at both ends on an alumina substrate. The bridges are periodically deflected in out-of-plane direction between heat source and sink by a miniature motor. By designing a curved geometry of heat sink, the bridge is deflected in mechanical contact with the heat sink causing a stress-induced martensitic transformation. The geometry of heat source is designed to be flat resulting in stress-release and thus undercooling during mechanical contact. Thus, periodic cycling results in the desired pumping of heat from source to sink. In order to increase efficiency, mechanical work stored in the deflected bridge is recovered by designing two mechanically coupled bridges. Temperature evolution of heat source and sink is determined by Pt100 temperature sensors, while the device temperature is monitored by an infrared camera. After 100 cycles, a temperature change of 5 K in the sink and -4.4 K in the source is observed giving rise to a temperature difference of 9.4 K. The cooling power, estimated from the heat capacity of heat source, is 42 mW. The dissipated work due to mechanical hysteresis is 14.4 mW yielding a device coefficient of performance COP of 2.9.
12:15 PM - EE11.5.07
Proof of the Concept Elastocaloric Regenerator-Based Cooling Device
Jaka Tusek 1,Kurt Engelbrecht 1,Nini Pryds 1
1 Technical University of Denmark; DTU Energy Roskilde Denmark,Show Abstract
Nowadays, virtually all cooling systems (and heat pumps) are based on vapor-compression technology, which despite continuous R&D exhibits relatively low energy efficiency and still uses gaseous refrigerants that can leak and affect the environment. Among alternative cooling technologies, a great emphasis in the last years was put on the research of caloric effect in ferroic materials under the influence of magnetic field (magnetocaloric effect), electric field (electrocaloric effect), mechanical stress (elastocaloric effect - ECE) and hydrostatic pressure (barocaloric effect).
Very recently, ECE has attracted a lot of attention due to its high transformation latent heat and consequently high adiabatic temperature change during the martensitic transformation. Although the ECE has been recognized as a potential cooling mechanism, there is still a lack of knowledge in designing practical elastocaloric cooling devices. Recently, some ideas have been presented, evaluated numerically [1, 2] and tested. Up-to-date, there are two working elastocaloric cooling systems: single-stage device developed by Schmidt et al.  where the maximum temperature span of 4 K was measured and the system using the heat recovery principle developed by Qian et al.  where a maximum temperature span of 1.5 K was measured.
In this talk we will present a new elastocaloric cooling system based on the active regeneration principle. Such a system is analogue to the active magnetic regenerator, which shows the greatest potential for exploitation of the magnetocaloric effect in a magnetic refrigerator. The system consists of an elastocaloric regenerator (made of a set of elastocaloric Ni-Ti plates), two external heat exchanges, a heat-transfer fluid, a fluid displacement system, and an actuator to (un)load the elastocaloric material. The elastocaloric plates are gripped at both ends and strained (loaded) to perform the austenitic–martensitic transformation, causing the elastocaloric plates to heat up. In the second step the fluid is pumped through this heated material (regenerator) to the hot heat exchanger (HHEX) where it rejects heat to the surroundings. In the next step the materials is unloaded and thus cools down. In the final step the fluid is pumped through the regenerator in the counter-flow direction and cooled fluid is able to absorb heat in the cold heat exchanger (CHEX). These four operational steps are continuously repeated, which causes a temperature profile along the length of the regenerator in the fluid flow direction and establishes a temperature span between HHEX and CHEX.
The system development, its operational principle and the preliminary results (the temperature span and cooling power at different operating conditions) will be presented and discussed.
 Tušek et al., Adv. Energy Mater., 5(13), 2015
 Qian et al., Int. J. Refrig., 56, 2015
 Schmidt et al., Int. J. Refrig., 54, 2015
 Qian et al., International Congress of Refrigeration, 2015
12:30 PM - EE11.5.08
Elastocaloric Systems and Materials
Yunlong Geng 1,Suxin Qian 2,Jan Muehlbauer 2,Jiazhen Ling 2,Yunho Hwang 2,Reinhard Radermacher 2,Ichiro Takeuchi 1
1 Materials Science and Engineering Univ of Maryland College Park United States,2 Mechanical Engineering University of Maryland College Park United StatesShow Abstract
We have demonstrated prototypes of elastocaloric cooling systems using shape memory alloys (SMAs). A 100-W prototype was designed and built based on two sets of NiTi tube bundles. The NiTi tubes are compressed alternatingly using an actuator while heat exchange water is flowing through them. The latent heat of the NiTi tubes was directly measured to be 10 J/g under 4.0% of compressive strain in the cooling experiment. The cooling capacity of 65 W and ΔT of 4.2 K was achieved for the prototype.
We are also carrying out search of replacement SMAs for elastocaloric cooling. Cu-based SMAs have the advantage that they require much smaller stress and are less expensive than NiTi. The elastocaloric effect of two chosen Cu-based SMAs, Cu68Al16Zn16 (CuAlZn) and Cu73Al15Mn12 (CuAlMn) under compression was studied at ambient temperature. Upon unloading from 4% strain, the highest adiabatic temperature change (ΔTad) of 4.0 K for CuAlZn and 3.9 K for CuAlMn were obtained. When compared to the typically required stress of 900 MPa for NiTi, the stress at 4.0% strain for CuAlMn and 3.5% strain for CuAlZn were 120 MPa and 430 MPa, respectively. The area enveloped in the stress-strain hysteresis corresponds to the input work required to deliver cooling out of elastocaloric materials in the work recovery mode. The typical measured area corresponds to 0.2 J/g for CuAlMn and 0.8 J/g for CuAlZn alloy. In comparison, it is 0.5 J/g for typical NiTi SMA. The latent heat, determined by differential scanning calorimetry, was 4.3 J/g for CuAlZn and 5.0 J/g for CuAlMn. The coefficient of performance of materials (COPmat) can be obtained by dividing the latent heat with the input work. Compared to COPmat of 15~18 for NiTi in the compression mode, we obtain COPmat = 6.4 for CuAlZn and 13.3 for CuAlMn.
EE11.6: Session V
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 127 A
2:45 PM - *EE11.6.01
Giant Barocaloric Effects in Ferrielectric Ammonium Sulphate
Pol Lloveras 2,Enric Stern-Taulats 3,Maria Barrio 2,Josep Lluis Tamarit 2,Sam Crossley 4,Wei Li 5,Vladimir Pomjakushin 6,Antoni Planes 3,Lluis Manosa 3,Neil Mathur 1,Xavier Moya 1
2 Universitat Politecnica de Catalunya Barcelona Spain,3 Universitat de Barcelona Barcelona Spain4 Stanford University Stanford United States5 HUST Huazhong China6 Paul Scherrer Institute Villigen Switzerland1 University of Cambridge Cambridge United KingdomShow Abstract
Giant barocaloric effects driven by hydrostatic pressure have been suggested for cooling applications, but they are only seen in a small range of magnetic materials that are relatively expensive. Here I will present pressure-dependent calorimetry data to demonstrate giant barocaloric effects in ferrielectric ammonium sulphate, which is made of cheap abundant elements [Lloveras et al., Nature Communications, in press].
3:15 PM - EE11.6.02
Pyroelectric and Electrocaloric Effects in Epitaxial Ferroelectric Thin-Films – Towards Advanced Materials and Measurements
Shishir Pandya 1,Bikram Bhatia 2,Anoop Rama Damodaran 1,Joshua Agar 1,Karthik Jambunathan 3,Vengadesh Kumara Ramakrishnan Mangalam 3,Lane Martin 4
1 Materials Science and Engineering University of California Berkeley Berkeley United States,2 Mechanical Engineering Massachusetts Institute of Technology Cambridge United States3 Materials Science and Engineering University of Illinois Urbana Champaign Urbana United States1 Materials Science and Engineering University of California Berkeley Berkeley United States,4 Materials Science Division Lawrence Berkeley National Laboratory Berkeley United StatesShow Abstract
There is a growing need for new ways to manipulate heat with materials. Ferroelectric materials, which possess a strong spontaneous polarization, present a number of opportunities in this space. In particular, one can make use of the pyroelectric effect which is the variation of remnant polarization P of a material as a function of temperature T at constant electric field E [(∂P/∂T)E] for waste heat energy conversion and, conversely, the electrocaloric effect which is the variation of T as a function of E at constant entropy S [(∂T/∂E)S] for solid-state cooling. Despite such prospects, the development of pyroelectric and electrocaloric materials has remained limited due to inadequate pathways to enhance thermal-electrical responses in materials, the presence of thermal-electrical losses, imprecise measurement techniques, and intrinsic material limitations. In this talk, we will address our recent work in developing a comprehensive understanding of polarization-heat interactions in complex ferroelectrics and will explore some challenges that have faced the community (including a lack of fundamental materials understanding, characterization methods, and adequate fabrication methodologies). We will explore the fundamentals of field- and temperature-dependent response of ferroelectrics which are known to exhibit large pyroelectric/electrocaloric responses and examine material design algorithms that can allow for maximization of such effects via control of both electrical/dielectric and pyroelectric responses, domain structures, and much more. We will discuss how designer domain structures and compositional gradients can be used to enhance and independently tune material properties thereby enabling the highest figures of merit observed to date. In particular, we will explore the use of composition- and strain-gradients in Ba1-xSrxTiO3 and PbZr1-xTixO3 thin films to generate large spatial gradients in spontaneous polarization (potentially in excess of 30 µC/cm2 across a 100 nm thick film). Such compositionally-graded films address two major problems: 1) the polarization gradient immobilizes defect-related space charge thereby inhibiting dielectric losses (tan δ
3:30 PM - *EE11.6.03
Neutron Diffraction Studies on Magnetostructural Transition and Barocaloric Effect in Mn-Co-Ge-In Alloys
Feng-Xia Hu 1,Qingzhen Huang 2,Yingying Zhao 1,Rongrong Wu 1,Lifu Bao 1,Jirong Sun 1,Baogen Shen 1
1 State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences Beijing China,2 NIST Center for Neutron Research, National Institute of Standards and Technology Gaithersburg United StatesShow Abstract
Recently, the ternary metallic compounds MM'X with hexagonal Ni2In-type structure have attracted much attention due to their rich magnetic and structural properties.1-3 The optimized compositions with concurrent magnetic and structural transitions showing a large magnetocaloric effect (MCE) have been discovered. In addition to the realization of magnetostructural transition, Tmstr , through introducing smaller atoms or vacancies, our recent studies revealed that introducing larger atoms with fewer valence electrons can also lower the crystallographic transition, Tstru , and create magnetostructural transition. Indium (In) atom has a larger atomic radius but fewer valence electrons than Mn, Co, or Ge. We found that the replacement of Mn, Co, or Ge by a little amount of In can also shift the Tstru to lower temperature, thus magnetostructural transition appears and large MCE shows up. High resolution neutron diffraction was performed to study the crystal and magnetic structures as functions of temperature, magnetic field, and pressure. It was found that the negative expansion of the unit cell volume across the Tmstr can be as large as △V/V∼-3.9% for a Mn-Co-Ge-In alloy, and a hydrostatic pressure can push the Tmstr to lower temperature at a rate of 7.7 K/kbar, indicating the materials may also show giant barocaloric effect. The evaluated entropy change under a pressure of 3 kbar reaches 52Jkg-1K-1, which exceeds that of most other materials. Careful refinements and analysis showed that external pressure stabilizes the hexagonal phase through shortening the Mn-Mn interlayer distance and strengthening the covalent bonding between Mn-Mn atoms.
On the other hand, these materials have rarely been considered as negative thermal expansion (NTE) materials to meet the urgent demand in industries though they surely display pronounced negative lattice expansion across the Tmstr . The reason is partially due to the limited phase transition window. By using a few percents of epoxy to bond the powders, we introduced residual stress and realized the broadening of structural transition by utilizing the specific characteristics of lattice softening enforced by the stress. As a result, giant NTE (not only the linear NTE coefficient α but also the operation-temperature window) has been achieved. For example, the average`α as much as -51.5×10-6/K with an operating temperature window as wide as 210K from 122 to 332K have been observed in a bonded compound.3
This work was supported by the National Basic Research Program of China (2014CB643700), the National Natural Sciences Foundation of China (51531008,51271196,11274357), and the "Strategic Priority Research Program B (XDB07030200)" and the Key Research Program of the Chinese Academy of Sciences.
 Liu, E. K. et al. Nat Commun. 3:873 doi: 10.1038/ncomms 1868 (2012).
 Caron, L. et al. Phys. Rev. B. 84, 020414 (2011).
 Zhao, Y.Y., Bao L.F., Hu, F.X, et al, J. Am. Chem. Soc., 5, 137 (2015).
4:30 PM - *EE11.6.04
Towards Multicaloric Refrigeration in Ni-Mn-Ga-Co/PMN-PT Heterostructures
Benjamin Schleicher 2,Stefan Schwabe 1,Annet Diestel 1,Anja Waske 1,Ruben Huehne 1,Peter Walter 4,Ludwig Schultz 2,Sebastian Faehler 2
1 IFW Dresden Dresden Germany,2 Institute for Solid State Physics TU Dresden Dresden Germany,1 IFW Dresden Dresden Germany3 Deutsches Elektronen-Synchrotron DESY Hamburg Germany,4 2nd Institute of Physics B and JARA-FIT RWTH Aachen Aachen GermanyShow Abstract
One of today’s challenges is a more efficient use of energy and in particular industrial and private cooling applications offer a large potential for improvement. For this issue various solid-state cooling cycles have been proposed, which rely on magnetocaloric, electrocaloric or elastocaloric effects. Giant caloric effects are observed in these ferroic materials in vicinity of a first order phase transition. A drawback, however, is the narrow usable temperature range. In order to tune the transition temperature we present multicaloric heterostructures consisting of magnetocaloric Ni -Mn-Ga-Co epitaxial films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN-PT) substrates. Applying an electric voltage to the substrate allows straining the film and by a stress induced martensitic transformation the transition temperature can be controlled. To probe the suitable magnetic and electric field range at different temperatures we present in-situ synchrotron diffraction experiments as well as SQUID measurements. We consider these multicaloric films to be of particular interest for solid state refrigeration since their high surface to volume ratio allows fast heat transfer and high cycling frequencies which leads to higher cooling power using less material.
This work is supported by DFG through SPP 1599 www.FerroicCooling.de.
5:00 PM -
5:15 PM - EE11.6.05
Electrocaloric Cooling in PVDF-Related Ferroelectric Polymers: First-Passage Kinetic Monte Carlo Analysis
Ying-Ju Yu 1,Alan McGaughey 1
1 Carnegie Mellon University Pittsburgh United States,Show Abstract
The objective of this study is to apply multi-scale modeling to explore the electrocaloric (EC) effect in PVDF-related ferroelectric polymers, which have application in active cooling of microsystems. The EC effect is the temperature rise and drop in some ferroelectric materials due to changes in the configurational entropy when an external electric field is applied and removed. The temperature change can be predicted using the polarization hysteresis loop and Maxwell relations.
We apply a first-passage kinetic Monte Carlo scheme to predict the polarization hysteresis loop of PVDF-related polymers. The polymer is modeled as a series of bi-directional permanent dipoles and induced point dipoles distributed on its monomer sites. The flipping of these dipoles due to the electric field is responsible for the polarization changes. Flipping the dipole moment of the polymer chain requires rotation of the individual monomers, each of which has its own energy barrier. This energy pathway is predicted from nudged elastic band method calculations for a variety of chain environments. We then use first-passage time analysis to convert the energy pathway into an average transition rate for the full polymer chain rotation. The transition rates for all chains are integrated into a kinetic Monte Carlo algorithm in which the polarization hysteresis loop is determined through an iterative process at each step of the electric field. At each step, polymer chain flips are chosen based on an N-fold algorithm that uses two random numbers. The higher the average transition rate of the polymer chain, the higher is its probability to flip. The polarization hysteresis loops at various external electric fields and operating temperatures are plotted and are used to extract the EC temperature change using Maxwell relations. Temperature changes of different copolymer and terpolymer compositions are predicted.
5:30 PM - EE11.6.06
Large Caloric Effects in Soft Materials
Zdravko Kutnjak 2,Maja Trcek 1,Marta Lavric 1,George Cordoyiannis 1,Bostjan Zalar 2,Qiming Zhang 3
1 Jozef Stefan Institute Ljubljana Slovenia,2 The Jozef Stefan International Postgraduate School Ljubljana Slovenia,1 Jozef Stefan Institute Ljubljana Slovenia3 Materials Research Institute The Pennsylvania State University University Park United StatesShow Abstract
Materials with large caloric effect have the promise of realizing solid state refrigeration which is more efficient and environmentally friendly compared to current techniques . A review of recent direct measurements of the large electrocaloric effect in liquid crystalline materials [2,3] and large elastocaloric effect in liquid crystal elastomers will be given. In liquid crystalline materials and mixtures of liquid crystals with functionalized nanoparticles the electrocaloric effect exceeding 8 K was found in the vicinity of the isotropic to smectic phase transition. Direct measurements indicate that the elastocaloric response of similar magnitude can be found in main-chain liquid crystalline elastomers . Both soft materials can play significant role as active cooling elements and parts of thermal diodes or regeneration material in development of new cooling devices.  Z. Kutnjak., B. Rozic. and R. Pirc., Electrocaloric Effect: Theory, Measurements, and Applications (Wiley Encyclopedia of Electrical and Electronics Engineering) 2015, p. 1-19.  I. Lelidis and G. Durand. Phys. Rev. Lett. 1996, 76, p 1868.  X.-S. Qian et al., Adv. Funct. Mater. 23, 2894 (2013).  A. Lebar, G. Cordoyiannis, Z. Kutnjak, B. Zalar, Adv. Polym. Sci. 250, 147 (2012).
5:45 PM - EE11.6.07
Structural and Ferroelectric Characterization of Freestanding 0.9 Pb(Mg1/3Nb2/3)O3- 0.1PbTiO3 Thin-Films for Direct Measurements of the ECE
Michael Mietschke 2,Christian Molin 3,Sylvia Gebhardt 3,Yang Zhang 1,Fei Ding 1,Stefan Abel 4,Jean Fompeyrine 4,Paul Chekhonin 2,Sebastian Faehler 2,Kornelius Nielsch 2,Ludwig Schultz 2,Ruben Huehne 1
1 IFW Dresden Dresden Germany,2 TU Dresden Dresden Germany,3 Department of Smart Materials and Systems Fraunhofer Institute for Ceramic Technologies and Systems Dresden Germany1 IFW Dresden Dresden Germany4 Materials, Integration and Nanoscale Devices (MIND)Team IBM Research GmbH Zurich SwitzerlandShow Abstract
Nowadays, significant efforts are made to develop environmentally friendly techniques in order to satisfy the huge demand of cooling power in almost all industrial and private areas. One emerging technology is the use of solid state cooling with electrocaloric (EC) materials. These materials show a remarkable temperature change by applying an electric field adiabatically, which is known as the EC effect. A prominent example are Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) compounds, which are typically used for high performance actuator applications due to its outstanding piezoelectric properties. As the structural and functional properties of these materials are well-known they might serve as a suitable model system to study the interplay between microstructure and EC properties. Epitaxial films are a useful tool to analyze this correlation in more detail in order to optimize the performance of these materials. A crucial point to determine the EC properties directly is to minimize the influence of the heat capacity of the substrate, which is realized by releasing the PMN-PT film from the template.
Therefore, epitaxial 0.9PMN-0.1PT films were grown by pulsed laser deposition on (001)-oriented STO buffered Si wafers as well as on SrTiO3 (STO) single crystalline substrates using an epitaxial La0.7Sr0.3Co3 buffer as bottom electrode and additional Au top electrodes on the surface of the PMN-PT layer. The PMN-PT film was released from the substrate by selective wet etching via channels from the top side. The particular PT content was chosen to get a ferroelectric phase transition close to room temperature making these materials interesting for solid state cooling applications under ambient conditions.
The structural properties are studied by high resolution x-ray diffraction, atomic force microscopy and transmission electron microscopy. Dielectric properties as the relative permittivity and the dielectric loss are determined in dependence of temperature and frequency to verify the ferroelectric quality. The determination of the EC properties was performed by using temperature dependent polarization measurements at different electric fields. Characteristic values for the electrocaloric effect as the entropy change and the resulting temperature change were calculated out of these measurements by the indirect method. Direct measurements will be performed with a high frequency setup, at which temperature changes are detected by an infrared sensor.
This work is supported by DFG priority program 1599 “Ferroic cooling”.