Intelligent self-actuating lead-free cooling ceramics based on A-site defect engineering

Current interests in electrocaloric (EC) and electromechanical (EM) effects have been stimulated by the discovery that self-actuating electrocaloric materials designed by using the electrostrain and entropy change ( Δ S ) characteristics of relaxor ferroelectrics are particularly appealing for applications in intelligent refrigeration devices. Herein, the lead-free Bi _0.5Na _0.5TiO ₃-based (BNT) ceramics designed by A-site defect engineering (ADE) can realize the collaborative EM and EC responses, e.g. obtaining electrostrain ∼ 0.47%, electrostrictive coefficient ∼ 0.031 m ⁴ C ^{− 2} and EC temperature change ∼ -0.512 K at room temperature. The temperature-dependent polarization electric current behaviors and local structures of ADE system show slowly-evolving nonergodic-ergodic transitions, corresponding to the EC and EM behaviors with a wide operating temperature range (i.e. electrostrain > 0.3% and electrostrictive coefficient > 0.030 m ⁴ C ^{− 2} within 105 °C, EC temperature change > 0.400 K within 50–125 °C). Landau theory shows that ADE method can reduce the barrier of high temperature disturbance. Furthermore, the uniform distributions of sodium and oxygen vacancies are conducive to the electric field response and orientation of the local dipoles. Most importantly, this work will further facilitate the development of self-actuating refrigeration materials/devices and provide an alternative concept to combine EM and EC effects by introducing A-site defects.