8 - Electrocaloric effect in relaxor ferroelectrics

Abstract

Relaxor ferroelectrics provide in a broad temperature range a large and reversible polarization change due to contributions to polarization not present in ordinary ferroelectrics, no hysteresis of heating and cooling, and a small P-E hysteresis loss. They possess a much larger temperature coefficient of dielectric permittivity than classical ferroelectrics. For all these reasons, relaxors are promising for EC applications. In general, the high dielectric response of relaxor ferroelectrics is attributed to the presence of nanometer-sized polar structures in the material’s bulk, the so-called polar nanoregions (PNRs). We discuss the evolution of polar nanoclusters with temperature. Relaxors are created by isovalent or aliovalent substitution of the A- or B-sites in normal ABO3 ferroelectrics, in tungsten bronzes, and in Aurivillius phases. A general overview of the EC effect in relaxor ferroelectric materials is given.