The Impact of Hysteresis on the Electrocaloric Effect at First‐Order Phase Transitions

• Published in: physica status solidi (b) Vol. 255; no. 2
• Main Authors: Marathe, Madhura, Ederer, Claude, Grünebohm, Anna
• Format: Journal Article
• Language: English
• Published: 01.02.2018
• Subjects: BaTiO3; electrocaloric effect; first‐order phase transitions; hysteresis; molecular dynamics simulations
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.201700308

We study the impact of thermal hysteresis at the first‐order structural/ferroelectric phase transitions on the electrocaloric response in bulk BaTiO3 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 discontinuous transitional part, stemming from the jump in entropy at the first order phase transition, and a continuous part, due to the 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 ≈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. As shown here, the calculated electrocaloric temperature change for BaTiO3, close to the paraelectric–ferroelectric transition, differs significantly for small fields when the field is applied or removed. Better understanding of such an effect is required for applications. Therefore, using a first‐principles‐based effective Hamiltonian, the authors examine the effect of thermal history of the sample on the electrocaloric effect at small fields and resultant irreversibility within the coexistence region.