Effects of La occupation site on the dielectric and piezoelectric properties of [Bi0.5(Na0.75K0.15Li0.10)0.5]TiO3 ceramics
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The crystal structure, phase transition and ferroelectric (FE)/piezoelectric properties were investigated for three types of La-doped [Bi0.5(Na0.75K0.15Li0.10)0.5]TiO3 ceramics. The dielectric measurements showed that the transition between FE and antiferroelectric (AFE) phases near 180 °C became pronounced by La addition, and the maximum permittivity was observed at 360 °C in La-doped samples, whereas at 290 °C in non-doped samples. Normal FE and excellent piezoelectric properties were observed by P–E hysteresis loop and piezoelectric measurements in samples without vacancy. However, when the A-site or B-site vacancies were formed, the temperature range of AFE phase extended even appeared at room temperature, which resulted in the presence of deformed P–E curves and decrease of piezoelectric properties. It was suggested that the AFE phase originated from the decoupling effect between BO6 octahedra in ABO3 perovskites due to the A-site and/or B-site vacancies.