Caloric effects in ferroics with antiferroelectric-ferroelectric phase competition and other materials

Caloric effects are associated with a reversible change in temperature under application or removal of external fields, such as electric, magnetic, or stress fields. Ferroics often exhibit large caloric responses which typically originate from the existence of structural phase transitions. Here we focus on caloric effects in ferroics with antiferroelectric-ferroelectric phase competition, the role of quantum effects in the caloric responses, and some exotic caloric effects predicted from first-principles-based simulations. Antiferroelectrics are interesting for caloric effects investigation since they develop antipolar ordering and exhibit dielectric constants comparable to those of ferroelectrics. We report several features of caloric effects in a prototypical antiferroelectric PbZrO₃: negative sign of electrocaloric effect in the antipolar phase, existence of a scaling law for the electrocaloric change in temperature, and prediction of highly tunable piezocaloric effect. Interestingly, PbZrO₃ can develop ferroelectric phases at the nanoscale as the temperature is lowered. Transition into a ferroelectric phase results in a large change in polarization which favors electrocaloric response. A combination of direct and indirect simulations is used to predict electrocaloric effect of up to 15 K in PbZrO₃ thin films. To the best of our knowledge, all current computational approaches utilize classical framework. We propose a semiclassical approach to direct simulations of caloric effects that takes into account quantum behavior of the heat capacity. Its application to prototypical ferroelectrics reveals a severe underestimation of electrocaloric change in temperature at low temperatures by classical simulations and offers a way to design caloric composites. Finally, we report our findings on some unusual caloric effects, such as flexocaloric effect and elastocaloric effect in nonferroics.