Enhanced room-temperature electrocaloric performance by both multiphase coexistence and diffused phase transition in (Ba0.65Sr0.3Ca0.05)(SnxTi1−x)O3 ferroelectric ceramics†

Electrocaloric (EC) solid-state refrigeration has been widely studied owing to its advantages of low energy consumption, environmental friendliness, and high refrigeration efficiency, but it has the challenges of small adiabatic temperature change (ΔT) near room temperature and narrow working temperature span (T_span). ΔT is associated with ferroelectric domain configuration, which can be modified by multiphase coexistence, while the operating temperature region can be extended by a diffused phase transition. In this work, tin was introduced in (Ba_0.65Sr_0.3Ca_0.05)TiO₃ ceramics to improve their EC performances. The introduction of Sn⁴⁺ effectively adjusted their phase-transition temperature and increased their breakdown field strength, which were highly beneficial for achieving a substantial ΔT. The highest ΔT of 1.79 K (indirect) and 2.18 K (direct) at 20 °C appeared in the (Ba_0.65Sr_0.3Ca_0.05)(Sn_0.02Ti_0.98)O₃ sample. The high electrocaloric effect (ECE) with a large temperature span near room temperature was obtained by modifying the phase transition temperature. Multiphase coexistence not only increased the number of ferroelectric domains (dipolar entropy) but also flattened the energy landscape to favor an easy polarization rotation. Thus, the ceramic samples prepared in this work have proven to be promising candidates for solid-state cooling.