Phase-composition and temperature dependence of electrocaloric effect in lead-free Bi0.5Na0.5TiO3-BaTiO3-(Sr0.7Bi0.2□0.1)TiO3 ceramics

The (0.94-x)Bi0.5Na0.5TiO3-0.06BaTiO3-x(Sr0.7Bi0.2□0.1)TiO3 (BNT-BT-xSBT, 0 ≤ x ≤ 0.24) solid solution ceramics were synthesized via a conventional solid-state reaction method and the correlation of phase structure, piezoelectric, ferroelectric properties and electrocaloric effect (ECE) was investigated in detail. The ECE in lead-free BNT-BT-xSBT ceramics was measured directly using a home-made adiabatic calorimeter with maximum adiabatic temperature change ΔT = 0.4 K with x = 0.08 under the electric field E = 6 kV/mm at room temperature. The position of maximum ECE was found in the vicinity of nonergodic and ergodic phase boundary, where the maximum change in entropy occurs as a result of the field-induced phase transformation between the ergodic and long-range ferroelectric phase. Besides, the mechanism for the shift of ECE peak is discussed in detail. Finally, the temperature dependence of ECE for BNT-BT-xSBT (x = 0, 0.04 and 0.08) was also investigated. This work may present a guideline for designing BNT-based ferroelectric relaxor ceramics for EC cooling technologies.