Chapter 9 - Electrocaloric effect in polycrystalline ferroelectrics and its measurement methods

Abstract

For the great demand of specialized energy applications, ferroelectric (FE) materials offer a promising route to provide a high-efficiency and environmentally friendly solid-state refrigeration technology due to the special advantages of easy miniaturization, high energy conversion efficiency, and easy manipulation. Normally, in a polar material, the reversible isothermal entropy or adiabatic temperature change can be driven by the application or withdrawal of an external electric field. This phenomenon is called electrocaloric effect (ECE). The ECE was first observed in Rochelle Salt by Kobeko and Kurtschoatov in the 1930s. The achieved magnitude of ECEs was always unsatisfactory for practical applications until a giant ECE of ΔTmax=12K was observed in the PbZr0.95Ti0.05O3 thin film in 2006. Since then, numerous FE or anti-FE polycrystalline materials such as thin films, thick films, and bulk ceramics were developed to meet the requirements of the solid-state refrigeration technology. The rapid development of ECE researches depends on reliable ECE testing technologies, whose progress is also notable in recent years. This chapter gives an overview about the ECE in various polycrystalline FEs and its measurement methods.