Negative/positive electrocaloric effect in antiferroelectric squaric acid

Abstract

Using the previously developed model, we study the electrocaloric effect (ECE) in antiferroelectric crystals of squaric acid, where the low-temperature polarization reorientation by the external electric field has been earlier predicted to be a two-stage process with the intermediate ferrielectric phase. The T-E landscape of the model entropy is explored. The ECE, characterized by the electric Grüneisen parameter, is found to be negative in the antiferroelectric phase. In the ferrielectric phase, it is positive at low fields but becomes slightly negative below the transition to the ferroelectric phase. In the ferroelectric phase, the ECE is positive at all temperatures and fields. The negative EC temperature shift ΔT of the largest magnitude is predicted to be around −2.7 K at 200 kV/cm. The supercritical behavior of the Grüneisen parameter in the crossover region between two bicritical end points is studied.