Origins of the Inverse Electrocaloric Effect

Abstract

The occurrence of the inverse (or negative) electrocaloric effect, where the isothermal application of an electric field leads to an increase in entropy and the removal of the field decreases the entropy of the system under consideration, is discussed and analyzed. Inverse electrocaloric effects have been reported to occur in several cases, for example, at transitions between ferroelectric phases with different polarization directions, in materials with certain polar defect configurations, and in antiferroelectrics. This counterintuitive relationship between entropy and applied field is intriguing and thus of general scientific interest. The combined application of normal and inverse effects has also been suggested as a means to achieve larger temperature differences between hot and cold reservoirs in future cooling devices. A good general understanding and the possibility to engineer inverse caloric effects in terms of temperature spans, required fields, and operating temperatures are thus of fundamental as well as technological importance. Here, the known cases of inverse electrocaloric effects are reviewed, their physical origins are discussed, and the different cases are compared to identify common aspects as well as potential differences. In all cases the inverse electrocaloric effect is related to the presence of competing phases or states that are close in energy and can easily be transformed with the applied field.

Indirect Electrocaloric Evaluation: Influence of Polarization Hysteresis Measurement Frequency

“…As reviewed, the artifacts of the indirect method may cause large uncertainties in ECE calculation, such as violation of the isostress and isofield conditions (especially in the case of thin films clamped to a substrate), extraction of unsuitable P ( T ) curves, and use of unsaturated P – E loops for evaluation . Note that in polycrystalline ferroelectric ceramics, the applied electric fields might be insufficient to fully pole the ceramics at low temperatures due to the existence of complex domain structures, especially for high frequencies.…”

A thermodynamic approach to rate-type models in deformable ferroelectrics

“…Hence, a decrease (increase) in the strength of an externally applied electric field yields a decrease (increase) in temperature. Nevertheless, a positive slope P is also possible if P and E are antiparallel, a situation that would correspond to an inverse electrocaloric effect [23].…”

Impact of domains on the orthorhombic-tetragonal transition of BaTiO3 : An ab initio study

“…For potential applications, not only thermal hysteresis and character of the transition but also their coupling to an external field is relevant and would determine the functional properties. For example, it has been discussed in the literature that giant caloric and piezoelectric responses are possible for a fieldinduced phase transition [2,22,34,35]. Therefore, we study the effect of an applied field on the evolution of multidomain phases as a function of temperature as well as the density of domain walls.…”