Lead-Free (1 - x)Ba(Zr0.2Ti0.8)O3 - x(Ba0.7Ca0.3)TiO3‑Based Ferroelectrics with Diffuse Phase Transitions for Sustainable Electrocaloric Applications.

The electrocaloric effect of a ferroelectric material is an effective technique for solid-state refrigeration. Although the peak value of the adiabatic temperature change (ΔT) due to the electrocaloric effect in normal ferroelectrics is found near the Curie point (T c), ferroelectrics with a diffuse phase transition are always desirable due to their wide temperature span of ΔT. In this work, the electrocaloric effect in sustainable Pb-free weak relaxor ferroelectrics, (1 - x)-Ba-(Zr0.2Ti0.8)-O3 - x(Ba0.7Ca0.3)-TiO3 (x = 0.19 and 0.21), with diffuse phase transition is reported. The diffuseness of each composition is determined based on the fitting of the temperature-dependent dielectric permittivity data to the Lorenz-type quadratic law. Interestingly, the maxima of ΔT of the compositions are observed at much higher temperatures than the temperature at maximum dielectric permittivity (T m) and freezing temperature (T f), which work as the effective T c of a relaxor ferroelectric. The wide temperature span (40 K) and high ΔT (0.8 K) of the x = 0.19 composition show the potential of this material for solid-state refrigeration applications. Moreover, the effects of diffuse phase transition on ΔT and its temperature span are discussed in (1 - x)-Ba-(Zr0.2Ti0.8)-O3 - x(Ba0.7Ca0.3)-TiO3-based ferroelectrics, which will help to design Pb-free electrocaloric materials with a diffuse phase transition for a wide working temperature range.