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Taking the temperature of phase transitions in cool materials
Scientific discussion meeting organised by Professor Neil Mathur, Dr Xavier Moya and Dr Sohini Kar-Narayan
Large thermal changes can arise when phase transitions are driven by magnetic fields, electric fields, or stress fields. These three effects arise in overlapping sets of materials, but have traditionally been studied separately. This meeting will promote scientific cross-fertilisation, and assess the potential of the materials for practical cooling applications.
Recorded audio of the presentations will be available on this page after the event and the papers will be published in a future issue of Philosophical Transactions A.
Attending this event
This event is intended for researchers in relevant fields and is free to attend. There are a limited number of places and registration is essential. An optional lunch is offered and should be booked during registration (all major credit cards accepted).
Enquiries: Contact the events team.
Organisers
Schedule
Chair
Emmanuel Defay, Luxembourg Institute of Science and Technology (LIST), Luzembourg
Emmanuel Defay, Luxembourg Institute of Science and Technology (LIST), Luzembourg
Emmanuel Defay has been working on the integration of dielectric and piezoelectric materials into Microsystems for 19 years. He completed his PhD at INSA Lyon (Fr.) in 1999 and stayed with CEA LETI Grenoble (Fr.) from 2000 to 2014. He is now leading the group "Ferroic Materials for Transducers" at the Luxembourg Institute of Science and Technology (Lu.) where he arrived in 2014. His scientific interests are mostly in piezoelectric films and electrocaloric devices. From 2010 to 2012, he was invited scholar in Pr Mathur's team at the University of Cambridge (UK) to study the electrocaloric effect and more specifically its energy efficiency. Emmanuel has published two books, 100 scientific papers and filed 30 patents.
09:05 - 09:30 |
Design of polar-dielectrics for electrocaloric cooling
The direct and efficient coupling between the electric signals and the elastic, thermal, optical and magnetic signals in ferroelectrics makes them attractive for exploring a broad range of cross-coupling phenomena which have great promise for new device technologies. This talk will present the recent advances at Penn State in developing electrocaloric materials which may provide alternative cooling technology to the century old vapor compression cycle (VCC) based cooling. Electrocaloric effect (ECE), which is the temperature and/or entropy change of dielectric materials caused by the electric field induced polarization change, is attractive to realize efficient cooling devices. Recently, we demonstrated that large ECE can be achieved in several classes of ferroelectric materials with tailored nano- and meso-structures. Experimental results on the ECE in the relaxor ferroelectric polymers and general theoretical considerations for achieving large ECE will be presented. This talk will also discuss considerations on and present recent works in using nanocomposites to further enhancing the ECE beyond the pure relaxor polymers, on the giant ECE in a class of dielectric liquid, and in ferroelectric ceramics near the invariant critical point. The works related to developing the EC cooling devices, making use of the newly developed large ECE in ferroelectric materials and featuring high cooling power density and high efficiency, will also be presented. Dr Qiming Zhang, Pennsylvania State University, USA
Dr Qiming Zhang, Pennsylvania State University, USADr. Qiming Zhang: Distinguished Professor of Engineering of Penn State University, USA. The research areas in his group include fundamentals and applications of electronic and electroactive materials. During more than 20 years at Penn State, he has conducted research covering dielectrics and charge storage devices, electrocaloric effect and solid state cooling devices, polymer thin film devices, polymer MEMS, actuators, sensors, transducers, and electro-optic and photonic devices. He has over 400 publications and 15 patents in these areas. He is the recipient of the 2008 Penn State Engineering Society Premier Research Award, the 2015 Penn State Faculty Scholar Medal, and a Fellow of IEEE and a Fellow of APS. |
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09:45 - 10:15 |
Multicaloric propertires of P(VDF-TrFE-CTFE) terpolymer
In the framework of caloric materials, electrocaloric effect on the one hand and elastocaloric effect on the other hand may be used for cooling systems. Electrocaloric effect refers to the electric field driven entropy change whereas elastocaloric effect refer to strain-driven entropy change. In some materials, such as P(VDF-TrFe-CTFE) and P(VDF-TrFe-CFE) terpolymer, both effects may exist. In this presentation, the characterization of the electrocaloric effect of terpolymer is presented. It is based on two complementary direct characterizations. In a first experiment, the isothermal heat exchange is measured upon the application of electric field steps using modified Differential Scanning Calorimetry equipment. In a second experiment, the adiabatic temperature change is measured upon fast electric field variation using a thermal imaging camera. It is shown that both characterizations are consistent. In case of elastocaloric effect, the characterization technique is first presented and the results obtained on stretched terpolymer are presented and compared to other elastocaloric materials such as natural rubber. The entropy variation in case of electrocaloric effect is believed to be related to the polar phase whereas elastocaloric effect is better related to the amorphous phase entropy. Based on thermodynamics considerations, theoretical conditions for the additivity of both effects are finally presented and discussed Dr Gael Sebald, Université de Lyon, INSA-Lyon, LGEF, France
Dr Gael Sebald, Université de Lyon, INSA-Lyon, LGEF, FranceGael Sebald graduated with a Ph. D. degree in acoustics in 2004 from INSA-Lyon (Lyon, France) for his work on single crystals with ultra high electromechanical coupling. He was then a Japan Society for Promotion of Science fellow (JSPS) (2004-2005) for a post-doctoral position at Tohoku University (Japan) where he developed fabrication, modeling and characterization of metal-cored piezoelectric fibers. Since 2005, Gael Sebald is associate professor at INSA Lyon (Lyon, France). After several developments on electrocaloric materials characterization, he developed energy harvesting from temperature fluctuations using the same materials. In 2010, he was a one-year Invited Researcher Fellow from JSPS to work at Tohoku University (Japan) on nonlinear energy harvesting and MEMS energy harvesters. His main research interests are smart materials characterization and applications, hysteresis modeling, multiphysics coupling in smart materials (especially piezoelectric, electrostrictive and electrocaloric couplings), and energy harvesting on vibration and heat. |
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11:00 - 11:30 |
Electrocaloric effect of antiferroelectric thick films
When a sufficiently high external electric field is applied to an antiferroelectric (AFE) material, a ferroelectric state can be induced in AFE, and this phase transition is often accompanied by larger strains and polarization changes, and normally occurs at far lower temperature than its Curie temperature. Therefore, Pb-based AFE materials have attracted increasing attention for the potential applications in cooling devices through electrocaloric effect near room temperature. Thick (1-100 μm) films possess large breakdown strength that bulk materials lack and relatively large heat-sinking capacity compared with thin films. In this work, antiferroelectric (AFE) thick films (1 μm) of (Pb(1-3x/2)Lax)(Zr1-yTiy)O3 with x = 0.08 -0.14 and their compositionally graded multilayer thick films were deposited on LaNiO3/Si(100) substrates by using a sol-gel method. A large reversible adiabatic temperature change of ΔT = 25 ºC was presented in the PLZT thick film with x=0.08 at 127 ºC at 990 kV/cm and also a large reversible adiabatic ΔT (=28 ºC) was presented in the compositionally graded thick films at room temperature at 900 kV/cm. The refrigerant capacities (ΔT x ΔS) of the compositional graded thick films and single composition PLZT thick film with x = 0.08 show comparable values with the best thin films’ values. These properties of the thick AFE films indicate that the thick films have strong potential application in cooling devices. Dr Qi Zhang, Cranfield University, UK
Dr Qi Zhang, Cranfield University, UKDr Qi Zhang received the BSc from Wuhan University, Wuhan, China in 1982, the M Eng from Wuhan University of Technology, Wuhan, China in 1986 and the PhD degree from Chemistry Department, Monash University, Australia, in 1995. In 1996, he joined the Nanotechnology Group, Cranfield University as a Research Officer, where he continued his research into thin film preparation by sol-gel processing. These thin film materials include complex metal oxides with ferroelectric and piezoelectric properties. In 1999, he became a Senior Research Fellow and continued to develop sol-gel spin coating technology for various inorganic thin films. In 2007 he became a senior lecturer and started working on materials for energy storage and the fabrication of nanomaterials and devices. He is currently a visiting professor in Wuhan University of Technology recruited under Hubei “one hundred people” program. He is a fellow of Institute of Materials, Minerals and Mining, UK. He is also a charted scientist. He has authored or co-authored 150 journal and conference papers with h index 23 and several chapters in books. He edited the book “Electrocaloric Materials” by Springer in 2013. His main areas of research are Materials synthesis and functional materials, nanoink formulation for directly ink-jet printing. His research also includes synthesis of nanomaterials, and manufacturing membranes for CO2 capture. |
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12:45 - 13:15 |
Electrocaloric and elastocaloric effects in soft materials
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 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. Professor Zdravko Kutnjak, Jozef Stefan Institute, Slovenia
Professor Zdravko Kutnjak, Jozef Stefan Institute, SloveniaDr Kutnjak has obtained Ph.D. degree in physics in 1994 at the University of Ljubljana. After two years of postdoctoral work at Massachusetts Institute of Technology, Dr Kutnjak returned to Jozef Stefan Institute, where as a head of the laboratory for calorimetry and dielectric spectroscopy and Professor at the University of Ljubljana continues research of ordered and disordered systems. His work is mainly focused on relaxor ferroelectrics, multiferroics, liquid crystal elastomers and various confined systems. Presently, he is involved in research and development of materials for novel electrocaloric cooling technologies. |
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13:30 - 14:00 |
Trajectories through parameter space of electrocaloric lead scandium tantalate
Measurements of electrocaloric (EC) effects can be challenging in various ways. I will review a variety of strategies that have been developed to meet these challenges over the past decade, and present fresh measurement protocols using lead scandium tantalate. Notably, I will show how to deduce EC temperature change from adiabatic contours on maps of total entropy. Separately, I will show how equivalent results may be obtained from electrical measurements in which thermodynamic conditions are varied via the measurement timescale Sam Crossley, Stanford University, USA
Sam Crossley, Stanford University, USASam Crossley studied Natural Sciences at King's College, Cambridge as an undergraduate. His doctoral research at Cambridge with Professor Neil Mathur focussed on the electrocaloric properties of a variety of thin film and bulk materials and devices. His experimental work developed and applied bespoke measurement apparatus, and was supported by finite-element and analytical modelling of heat flow. He has authored scientific papers and review articles in the fields of electrocaloric materials and piezoelectric energy harvesting materials. His postdoctoral research on energy materials is with Professor Harold Hwang at Stanford University and SLAC National Accelerator Laboratory. |
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14:45 - 15:30 | Poster session |
Chair
Dr Gerald Brown, NASA Glenn Research Center, USA
Dr Gerald Brown, NASA Glenn Research Center, USA
Dr Brown is currently a Senior Research Engineer in the Rotating and Drive Systems Branch at the NASA Glenn Research Center, USA. He has degrees in physics from Rice University (BA 1959) and Case Western Reserve University (PhD 1977). He currently works on modeling and system analysis of turboelectric propulsion for transport aircraft and leads the current work on superconducting electrical systems for aero-propulsion. He has previously headed groups in aeroelasticity, magnetics and cryo-physics. He has previously worked on cryogenic and superconducting electromagnets, magnetic bearings, structural dynamics and magnetic refrigeration.
15:30 - 16:00 |
Energy efficient refrigeration near room temperature with transition metal based magnetic refrigerants
With the advent of giant magnetocaloric effects (MCE) that occur in conjunction with magneto-elastic or magneto-structural phase transition of first order(FOT), room temperature applications became feasible. In this context the MnFe(P,X) system is of particular interest as it contains earth abundant ingredients that are not toxic. This material family derives from the Fe2P compound, a prototypical example known since a long time to exhibit a sharp but weak FOT at 210 K (-63°C). In this hexagonal system, the Fe atoms occupy two inequivalent atomic positions referred as 3f (in a tetrahedral environment of non-metallic atoms) and 3g (pyramidal). One intriguing aspect is the disappearance of the magnetic moments of iron atoms on the 3f sites when crossing TC, whereas there is only a limited decrease on the 3g site. This observation has led to a cooperative description of the FOT linking the loss of long range magnetic order at TC with the loss of local moments on 3f. This mechanism has recently been shown to be at the origin of the G-MCE observed in MnFe(P,Si). The disappearance of the magnetic moments has been ascribed to a conversion from non-bonding 3f d electrons into a distribution with a pronounced hybridization with the surrounding Si/P atoms. Therefore, one can expect to adjust the properties of these compounds by substitutions on the non-metallic site. This solution has been used to optimize the properties of MnFe(P,Si) materials. Dr Ekkes Brück, TU Delft, Netherlands
Dr Ekkes Brück, TU Delft, NetherlandsEkkes Bruck is currently full professor at Delft University of Technology and head of section Fundamental Aspects of Energy and Materials. He has previously worked as a visiting professor at Department of Mechanical Engineering and at the Federal University of Santa Catarina, Florianopolis, Brazil. His research interests include magnetic materials, magnetic refrigeration, renewable energy, phase transitions, energy storage, energy conversion. |
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16:15 - 16:45 |
(Magneto)caloric refrigeration: Is there light at the end of the tunnel?
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 (a.k.a. thermoelastic), 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. Professor Vitalij Pecharsky, Ames Laboratory, USA
Professor Vitalij Pecharsky, Ames Laboratory, USAProfessor Pecharsky received B.S./M.S. in Chemistry in 1976 (with distinction) and Ph.D. in Inorganic Chemistry in 1979 from Ivan Franko National University of L’viv (formerly L’viv State University), Ukraine. Between 1979 and 1993 he held positions of Assistant and Associate Professor at the Department of Inorganic Chemistry. In 1993 he moved to Ames, Iowa and currently holds a rank of Anson Marston Distinguished Professor of Materials Science with the Department of Materials Science and Engineering at Iowa State University, and Faculty Scientist and Field Work Project Leader at the US Department of Energy Ames Laboratory. His research interests include synthesis, structure, and physical properties of intermetallic compounds containing rare earth metals, magnetostructural phase transformations, magnetocaloric effect, hydrogen storage materials, and mechanochemistry. He published over 400 papers and one book, holds 14 patents, and serves as an editor of the Journal of Alloys and Compounds and the Handbook on the Physics and Chemistry of Rare Earths. |
Chair
Dr Karl G. Sandeman, Brooklyn College, City University of New York, USA
Dr Karl G. Sandeman, Brooklyn College, City University of New York, USA
Karl Sandeman's research has focussed on understanding the structure-function relationship in magnetic materials, using a combination of experimental and theoretical techniques. His group has recently investigated tricritical metamagnetism and piezomagnetic effects in non-collinear antiferromagnets and the origins of magneto-elastic coupling in room temperature itinerant ferromagnets. Karl received his undergraduate degree and a PhD in low temperature condensed matter theory from the University of Cambridge and held a Royal Society University Research Fellowship from 2005-2013. From 2009-2015 he was a faculty member of the Department of Physics at Imperial College London where he was also the coordinator of "SSEEC" (http://www.sseec.eu) and "DRREAM" (http://www.drream.eu), two 3-year collaborative projects on room temperature magnetic cooling funded by the European Commission's Seventh Framework Programme. Karl joined the City University of New York in 2014, establishing a new research group at Brooklyn College.
09:00 - 09:30 |
Mastering hysteresis in magnetocaloric materials
A MCE materials parameter´s library including the (cyclic) adiabatic temperature ΔTad, entropy ΔS, heat capacity cp and thermal conductivity λ, of large number of candidate materials is presented. This data base comprises the most relevant magnetic refrigerants LaFeSi-, Heusler- and Fe2P-type compounds but also manganites, FeRh and others. Primary magnetocaloric properties are investigated, intrinsic and extrinsic contributions to hysteresis are analysed and secondary engineering properties are studied. Most importantly their cyclic behaviours, their dynamic responses to various magnetic field rates and effects of fragmentation are compared and from there develop strategies how to fabricate efficient heat exchangers suitable for application. Finally, our magnetocaloric test bench which allows the assessment of the above materials under real working conditions – the latter being quite different from the elaborated measurements protocols commonly employed – is described. Professor Oliver Gutfleisch, TU Darmstadt, Germany
Professor Oliver Gutfleisch, TU Darmstadt, GermanyProfessor Dr Oliver Gutfleisch is a full Professor for Functional Materials at TU Darmstadt and a scientific director at Fraunhofer IWKS (project group for Materials Recycling and Resource Strategies). His scientific interests span from new permanent magnets for power applications to solid state energy efficient magnetic refrigeration, ferromagnetic shape memory alloys, magnetoelastomers for adapted damping and actuation, magnetic nanoparticles for biomedical applications, and to solid state hydrogen storage materials with a particular emphasis on tailoring structural and chemical properties on the nanoscale. Resource efficiency on element, process and product levels as well as recycling of rare earth containing materials are in the focus of his work. He has published more than 290 papers in refereed journals, and has given more than 170 invited talks. In 2011 he was an IEEE Magnetics Society Distinguished Lecturer on the topic of Magnet Materials for Energy. He is on the Advisory Committees of the Int. Workshop on Rare−Earth Permanent Magnets and their Applications and of the Magnetic Refrigeration Intl. Working Party, on the IEEE Magnetics Society AdCom (2011-2013), and the TMS Magnetic Materials Committee. He is EU ERAMIN (Network on the Industrial Handling of Raw Materials for European Industries) advisor on substitution, a member of the EU ERECON (European Rare Earths Competency Network) Steering Committee and had visiting Professorships at Imperial College London and Chinese Academy of Science NIMTE Institute in Ningbo. |
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09:45 - 10:15 |
Magnetocaloric properties of ferromagnetic shape memory materials: from bulk to nano
Ferromagnetic shape memory materials, introduced in 1996 have constantly shown new emerging properties exploitable in different fields of application, including solid state refrigeration. Giant effects can be driven by external fields, i.e. magnetic field, pressure and stress and by their combined application, enabling their multifunctional exploitation. Two main physical properties underlie this challenging and rich phenomenology: a martensitic transformation (i.e. solid state diffusionless structural transition) and magnetically ordered states. The wide tunability of crystal structure, magnetic interaction, critical temperatures by suitable changes of composition in the most representative class of materials, the Heusler compounds, is of great interest. With respect to the bulk materials, thin films offer the possibility to be integrated in micro/nanosystems and could be at the basis of new–concepts nanoactuators, energy harvesters and solid-state microrefrigerators. In this talk the basic and functional properties of these compounds will be presented and their tailoring potential in bulk materials and thin films to improve their exploitation in solid state refrigeration and energy-related applications discussed. Dr Franca Albertini, Institute of Materials for Electronics and Magnetism (CNR), Italy
Dr Franca Albertini, Institute of Materials for Electronics and Magnetism (CNR), ItalyFranca Albertini is the Magnetic Materials group leader at the Institute of Materials for Electronics and Magnetism (IMEM) of the Italian National Research Council (CNR). Her research interests are focused on multifunctional magnetic materials for energy applications, memories and nanomedicine. She is author of 100 publications and more than 200 presentations at international conferences. She is member of the Administrative Committee of the IEEE Magnetic Society and of the Magnetism Panel of the European Physical Society. She is in the scientific advisory committees of the European School on Magnetism and of some international conferences on magnetism and magnetic materials. |
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11:00 - 11:30 |
Characterisation of the magnetocaloric transition
Materials exhibiting the magnetocaloric effect (MCE), in which a temperature change occurs in response to a change of magnetic field, have gained increasing interest for solid state magnetic cooling applications. Large MCE is often associated with coupled magnetostructural or magnetovolume effects, resulting in a first-order MC transition. Much interest has focused on materials with first-order transitions as they have large magnetic entropy and adiabatic temperature changes in response to magnetic field changes achievable using permanent magnets. First-order transitions are demarcated by a nucleation and growth process and consequently a region or period of coexistence of two phases which usually results in undesirable irreversibility, and magnetic and thermal hysteresis. When used in commercial-type cooling systems, cycling frequencies of at least a few Hz are imperative, with of course the desire for repeated cycling without degradation of the solid magnetocaloric coolant; all of these complicating factors associated with first-order transitions have to be considered. The study of time dependence and rate effects of the MCE transition is relevant to the potential for use as a practical magnetic refrigerant with reasonable operation frequencies. In this talk the use of microcalorimetry to determine the first order character of the transition will be discussed, and the use of Hall probe imaging and magnetometry to study the influence of geometry and thermal linkage on the evolution of the field driven magnetocaloric transition. Professor Lesley Cohen, Imperial College London, UK
Professor Lesley Cohen, Imperial College London, UKProfessor Lesley Cohen is a professor of solid state physics studying the fundamental behaviour of materials and devices with unusual electronic, optical, superconducting or magnetic properties for a variety of applications including solid state efficient and environmentally friendly magnetic refrigeration. Over a number of years her group has developed a suite of characterisation tools that have enabled unique insight into the behaviour of materials at low temperatures and high magnetic fields. She has published over 350 journal publications in her areas of interest. |
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11:45 - 12:15 |
Thermodynamics of multicaloric effects in multiferroic materials
Ferroic and multiferoic materials thermally respond to externally driven changes of ferroic properties. Usually these changes are induced either by application or removal of the field thermodynamically conjugated to a given property. The corresponding isothermal change of entropy and adiabatic change of temperature are commonly used to quantify the caloric response of the studied material. From this perspective we provide a general thermodynamic framework to deal with multicaloric effects in multiferroic materials. This is applied to the study of both magnetostructural and magnetoelectric multiferroics. Landau models with appropriate interplay between the corresponding ferroic properties (order parameters) are proposed for metamagnetic shape-memory and ferrotoroidic materials, which respectively belong to each class of multiferroics. The multicaloric effect is obtained as a function of the two relevant applied fields in each class of multiferroics. It is further shown that multicaloric effects comprise the contributions from caloric effects associated with each ferroic property and the cross-contribution arising from the interplay between these ferroic properties. The obtained results will be compared with available experimental data. Professor Antoni Planes, Universitat de Barcelona, Spain
Professor Antoni Planes, Universitat de Barcelona, SpainAntoni Planes is Professor of Condensed Matter Physics in the Department d'Estructura i Constituents de la Matèria at the Universitat de Barcelona, Catalonia. His recent research is focused on the study of phase transitions in ferroic and multiferroic materials with particular interest in the caloric effects associated with these transitions. He is also active in the study of the influence of disorder in phase transitions, with the aim of understanding precursor phenomena and avalanche criticality in externally driven systems. |
13:30 - 14:00 |
Thermoelastic cooling: mechanism, materials and systems
We are actively developing prototypes of thermoelastic (elastocaloric) cooling systems using mechanisms based on compression of shape memory alloys. In the latest design, we are compressing bundles of NiTi tubes while heat exchange fluid flows through the tubes. A key component is a heat recovery system implemented in order to maximize the efficiency of the heat exchange. We have observed cooling T of 4.5 K at 70 W, as directly measured in cooled water. We have demonstrated that when properly loaded, shape memory alloy tubes can survive up to at least ~ 0.3 million cycles without any degradation in cooling capacity. We will also discuss our efforts in developing alternative shape memory alloys. Professor Ichiro Takeuchi, University of Maryland, USA
Professor Ichiro Takeuchi, University of Maryland, USAIchiro Takeuchi is a Professor of Materials Science and Engineering and an Affiliate Professor of Physics at the University of Maryland. He obtained his PhD in Physics from the University of Maryland in 1996. He was a Postdoctoral Fellow at Lawrence Berkeley National Laboratory from 1996-1999. He joined the University of Maryland faculty in 1999. Takeuchi has served as a Visiting Professor at the University of Tokyo, Tokyo Institute of Technology, and Ruhr University, Bochum. He was a fellow of the Japan Science and Technology Agency from 2007 to 2008. Takeuchi won the Invention of the Year Award from the University of Maryland in 2010 for his invention of thermoelastic cooling, a novel alternative cooling technology. He also serves as a Chief Technology Officer for Maryland Energy and Sensor Technologies, a start-up dedicated to commercialization of thermoelastic cooling. Takeuchi is a fellow of the American Physical Society. |
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14:15 - 14:45 |
TiNi-based thin films for elastocaloric applications
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. Professor Eckhard Quandt, Kiel University, Germany
Professor Eckhard Quandt, Kiel University, GermanyEckhard Quandt received his diploma in physics and his Dr.-Ing. at the Technical University Berlin in 1986 and 1990, respectively, working on solid state physics and electron microscopy. Since 1991 he has worked on thin film smart materials and their applications at the Forschungszentrum Karlsruhe (1991-1999), at the Stiftung caesar (1999-2006)and since 2006 at the Christian-Albrechts-Universität zu Kiel, where he holds the Chair for Inorganic Functional Materials within the Institute for Materials Science at the Faculty of Engineering. Presently he is Dean of the Faculty of Engineering. Furthermore he is member of “acatech” the National Academy of Science and Engineering in Munich. |
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15:30 - 16:00 |
Large elastic strain and elastocaloric effect in an Fe-Pd alloy exhibiting a weak first-order martensitic transformation
A disordered Fe-31.2Pd (at%) alloy exhibits a weak first-order martensitic transformation from a cubic structure to a tetragonal structure near 230 K. This transformation is associated with significant softening of an elastic constant (C’), and the softening is probably due to band Jahn-Teller effect of the alloy. In this study, we have examined mechanical properties and phase diagram under compressive stress in the [001] direction by using a single crystal. The alloy shows an elastic-like behavior when the stress is applied above the transformation temperature. That is, the hysteresis between stress applying and removing processes is very small, and the residual strain is negligibly small. The stress-induced strain depends strongly on test temperature, and a large elastic-like strain of more than 6% appears when the stress is applied in the vicinity of the transformation temperature. Above the yield point, mechanical twinning with {111} type twinning plane is introduced in the specimen. The phase boundary between the parent and the martensite phases in the stress-temperature phase diagram seems to have a critical point (40MPa, 280K), above which the first order nature of the transformation completely disappears. In addition, because of significant temperature dependence of elastic-like strain, the alloy shows a high elastocaloric effect in a wide temperature range (175K<T<335K) for both the parent and the martensite phases. The refrigeration capacity calculated in this temperature range is 5MJ/m3. Professor Tomoyuki Kakeshita, Osaka University, Japan
Professor Tomoyuki Kakeshita, Osaka University, JapanProfessor Tomoyuki Kakeshita is a Professor in the Material Science and Engineering department at Osaka University. He is the Dean of Engineering and his research interests include phase transformation and magnetic transition in alloys and ceramics(3d and 4f), properties of materials under extreme conditions (high magnetic field, high pressure) and electronic structure (Band Calculation Phase Stability) |
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16:15 - 17:00 |
Mechanocaloric effects in ferroic materials
Mechanocaloric effects refer to isothermal entropy and adiabatic temperature changes of a body when subjected to an external stress. Depending on wether the stress is uniaxial or hydrostatic the effect is known as elastocaloric or barocaloric. Commonly these changes are tiny, but they can become very pronounced when a solid is in the vicinity of a ferroic phase transition which involves a structural change. Actually, a variety of materials undergoing purely structural and coupled (magneto-structural and electro-structural) transitions have already been reported to exhibit giant elastocaloric and barocaloric effects. The talk will cover some general aspects on the thermodynamics of mechanocaloric effects and how thermodynamic quantities can be extracted from different experimetal protocols. A critical comparative analysis of entropy and temperature changes reported for diverse giant magnetocaloric materials will also be presented. Professor Lluis Mañosa, Universitat de Barcelona, Spain
Professor Lluis Mañosa, Universitat de Barcelona, SpainLluis Mañosa received all his degrees (B.Sc. and PhD) from the Unversity of Barcelona in Catalonia. He was post-doctoral fellow at the University of Bath (UK) and at INSA, Lyon (France), and visiting professor at the Ames Laboratory (USA). Presently he is a Professor in Condensed Matter Physics at the University of Barcelona. His interests relate to structural and magnetic properties in solids. Recent research focuses on the study of phase transitions in solids displaying multifunctional properties. |