Origin of negative electrocaloric effect in Pnma-type antiferroelectric perovskites

TL;DR

This paper investigates the origin of the negative electrocaloric effect in Pnma-type antiferroelectric perovskites, revealing a new mechanism involving octahedral tiltings that explains the anomalous cooling behavior.

Contribution

It introduces a novel explanation for the negative electrocaloric effect in antiferroelectrics, emphasizing the role of octahedral tiltings, based on first-principle calculations.

Findings

Negative ECE can reach large magnitudes in BNFO.

Explicit consideration of octahedral tiltings is crucial for understanding ECE.

A new mechanism explains anomalous ECE beyond dipole canting.

Abstract

Anomalous electrocaloric effect (ECE) with decreasing temperature upon application of an electric field is known to occur in antiferroelectrics (AFEs), and previous understanding refers to the field-induced canting of electric dipoles if there is no phase transitions. Here, we use a first-principle-based method to study the ECE in Nd-substituted BiFeO3 (BNFO) perovskite solid solutions, which has the Pnma-type AFE ground state. We demonstrate another scenario to achieve and explain anomalous ECE, emphasizing that explicit consideration of octahedral tiltings is indispensable for a correct understanding. This mechanism may be general for AFEs for which the antipolar mode is not the primary order parameter. We also find that the negative ECE can reach a large magnitude in BNFO.