Caloric Effects in Ferroic Materials: New Concepts for Cooling

Abstract

Refrigeration is one of the main sinks of the German and European electricity consumption and accordingly contributes to worldwide CO 2 emissions. High reduction potentials are envisaged if caloric effects in solid materials are used. The recent discovery of giant entropy changes associated with ferroelastic phase transformations promises higher efficiency. Ferroic transitions enhance the entropy change of magneto-, elasto-, baro-, and electro-caloric effects. Furthermore, because the refrigerant is in a solid state, this technology completely eliminates the need for halofluorocarbon refrigerants having a high global-warming potential. The smaller footprint for operation and the scalable mechanism open up further applications such as cooling of microsystems. While the principal feasibility of magnetocaloric refrigeration is already evident, it requires large magnetic fields (>2 T) which hampers wide industrial and commercial application. It is expected that this obstacle can be overcome by materials with lower hysteresis and by using stress-or electric fields. In order to accelerate research on ferroic cooling, the Deutsche Forschungsgemeinschaft (DFG) decided to establish the priority program SPP 1599 in April 2011. In this article we will address the major challenges for introducing ferroic materials in practical cooling applications: energy efficiency, effect size, and fatigue behavior. Solid state cooling in this sense can be based on the following ''ferroic-caloric'' classes of materials: ferroelastic shape memory alloys, ferromagnetic shape memory alloys, and ferroelectric materials and their possible combinations in materials with ''multicaloric'' effects. The open questions require the interdisciplinary collaboration of material scientists, engineers, physicists, and mathematicians. 10 wileyonlinelibrary.com ß

Influence of epitaxial strain on elastocaloric effect in ferroelectric thin films

“…13 For instance, it was reported that the hysteresis loss can be lowered in Fe-Pd single crystal exhibiting a second-order like martensitic transition. 6 In addition, as the size of current shape-memory alloys shrinks towards the nano-scale, numerous problems and instabilities arise, including fatigue, micro-cracking, and oxidation.…”

“…[2][3][4][5][6][7][8][9][10][11] Moreover, due to the second-order nature of the phase transition, it is expected that the hysteresis loss and irreversibilities associated with latent heat vanish, which is of importance to enhance refrigerant efficiency. 5,12,13 In addition, the system can operate in a wide temperature window for all compressive substrates we investigated (see, e.g., the 60 K FIG. 1.…”

Multicaloric effect in ferroelectric PbTiO3from first principles

“…Moreover, given a relative abundance of extrinsic multiferroics among ferroics with multiple order parameters, such prediction may open an unusual route to solid state refrigeration advancement. Recent discoveries of giant caloric effects in some ferroic materials [1][2][3][4][5][6][7][8][9][10] have opened the door to the use of solidstate materials as an alternative to gases for conventional and cryogenic refrigeration 11 . The wide class of ferroics includes such diverse materials as ferromagnets and magnetic materials, ferroelectrics, ferroelastics and multiferroics.…”

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

“…Thus, the most widely used dopants to reduce the critical field are La 3+ , Ba 2+ , Ca 2+ on the Pb 2+ site and Sn 4+ , Ti 4+ and Nb 5+ on the Zr 4+ site 1,3 . The AFE/FE transition in PbZrO 3 -based perovskites is also associated with high entropy changes and electrocaloric/pyroelectric effects, which are very interesting for novel applications such as solid state cooling and pyroelectric energy harvesting [4][5][6][7] . For example, in Pb 0.97 La 0.02 (Zr 0.95 Ti 0.05 )O 3 a maximum reversible adiabatic temperature change of 8.5 • C has been obtained near the phase transition temperature together with a very large recoverable energy density of 12.4 J/cm 3 at room temperature 5 .…”