Flexocaloric effect in ferroelectric materials: methods of indirect evaluation

Abstract

Ferroelectric materials have great potential use for solid-state refrigeration. However, their working temperature is restricted to Curie temperature; the working temperature can be increased by the new component of strain gradient-driven caloric effect or flexocaloric effect (FCE). The FCE relies on the inhomogeneous strain of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). The strain gradient-induced polarization is defined by flexoelectric polarization coefficient and is utilized to estimate the FCE. As the FCE is a relatively new phenomenon, several ways can be used to calculate it. Different methods of flexocaloric quantification in ferroelectric materials (Pb(Mg1/3Nb2/3)O3 and Ba0.67Sr0.33TiO3) are discussed in the present work. The FCE can be obtained based on the measured properties and combination between the polarization and strain. This allows one to study the actual or net flexocaloric behavior in the material. It was found that the quantification of temperature change varies according to the method used for estimation. The experimental confirmation is required for validation of the proposed methods of estimation. Further, this work also discusses the possibility of other ways that are untouched by the research community. The analysis indicates a substantial untapped potential for solid-state refrigeration and warrants further research. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.