Phase-composition and temperature dependence of electrocaloric effect in lead-free Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3-(Sr_(0.7)Bi_(0.2)□_(0.1))TiO_3 ceramics

摘要

The (0.94-x)Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3-(Sr_(0.7)Bi_(0.2)□_(0.1))TiO_3 (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 = OAK 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 non-ergodic 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.