Large Strain with Small Hysteresis at High Temperature of Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃-BaZrO₃ Lead-Free Piezoelectric Ceramic

This study investigates the effects of temperature on the phase evolution and the electrical properties of the 0.77Bi_0.5Na_0.5TiO₃-0.22Bi_0.5K_0.5TiO₃-0.01BaZrO₃ lead-free piezoelectric ceramic. The ceramic is fabricated using a conventional solid-state reaction method. The crystal structure and microstructure of the sintered sample are analyzed at room temperature. The sample sintered at 1150 °C shows a single perovskite structure, dense microstructure, and a relative density of ~ 86%. The temperature-dependent electrical properties of the ceramic are studied in the temperature range of 25-125 °C. At room temperature, the 0.77Bi_0.5Na_0.5TiO₃-0.22Bi_0.5K_0.5TiO₃-0.01BaZrO₃ ceramic shows the nonergodic relaxor behavior with a tetragonal structure. A phase transition from a nonergodic relaxor to an ergodic relaxor phase happened in the 0.77Bi_0.5Na_0.5TiO₃-0.22Bi_0.5K_0.5TiO₃-0.01BaZrO₃ ceramic when the temperature increases above 116 °C. The electric-field-induced strain property of the 0.77Bi_0.5Na_0.5TiO₃-0.22Bi_0.5K_0.5TiO₃-0.01BaZrO₃ ceramic increases with a temperature coefficient of 0.367 pm/V/K. The thermal energy increases the maximum strain value and decreases the strain hysteresis of the 0.77Bi_0.5Na_0.5TiO₃-0.22Bi_0.5K_0.5TiO₃-0.01BaZrO₃ ceramic. At 125 °C, the ceramic shows a maximum electrostrain of ~ 505 pm/V with a minimum hysteresis of ~ 9%, suggesting a potential candidate for lead-free piezo-actuator applications.