The impact of hysteresis on the electrocaloric effect at first-order phase transitions

TL;DR

This study investigates how thermal hysteresis affects the electrocaloric effect in BaTiO₃ during first-order phase transitions, revealing a large, history-dependent temperature change that can be enhanced with stronger electric fields.

Contribution

The paper introduces a molecular dynamics simulation approach to separate and analyze the transitional and configurational contributions to the electrocaloric response at first-order phase transitions.

Findings

Large electrocaloric temperature change (~1 K) is mainly due to transition entropy.

The response depends on thermal history and is generally non-reversible.

Applying larger fields can overcome irreversibility caused by hysteresis.

Abstract

We study the impact of thermal hysteresis at the first-order structural/ferroelectric phase transitions on the electrocaloric response in bulk BaTiO$_3$ by performing molecular dynamics simulations for a first-principles-based effective Hamiltonian. We demonstrate that the electrocaloric response can conceptually be separated in two contributions: a transitional part, stemming from the discontinuous jump in entropy at the first order phase transition, and a configurational part, due to the continuous change of polarization and entropy within each phase. This latter part increases with the strength of the applied field, but for small fields it is very small. In contrast, we find a large temperature change of $\sim 1$ K resulting from the transition entropy, which is essentially independent of the field strength. However, due to the coexistence region close to the first order phase transition, this large electrocaloric response depends on the thermal history of the sample and is generally not reversible. We show that this irreversibility can be overcome by using larger fields.