Effects of A-site vacancy on the electrical properties in lead-free non-stoichiometric ceramics Bi0.5+x(Na0.82K0.18)0.5−3xTiO3 and Bi0.5+y(Na0.82K0.18)0.5TiO3

In order to create A-site vacancy in lead-free piezoelectric ceramics Bi0.5(Na0.82K0.18)0.5TiO3, non-stoichiometric ceramics Bi0.5+x(Na0.82K0.18)0.5−3xTiO3 and Bi0.5+y(Na0.82K0.18)0.5TiO3 were synthesized by a conventional solid state reaction method. The effects of A-site vacancies on the piezoelectric and ferroelectric performances of the ceramics were investigated and discussed. This investigation reveals that moderate A-site vacancies in the prepared ceramics enhance the piezoelectric performance of the ceramics. Bi0.505(Na0.82K0.18)0.485TiO3 ceramic possesses the highest piezoelectric properties and strongest ferroelectricity: piezoelectric coefficient d33 = 151 pC/N; electromechanical coupling factor kp = 29.8%; mechanical quality factor Qm = 124; remnant polarization Pr = 29.5 μC/cm2; coercive field Ec = 33.9 kV/cm. The depolarization of the BNT-based ceramics might be caused by phase transition from long-range ferroelectric to ergodic relaxor near Td.

► Moderate A-site vacancies can enhance the piezoelectric performance of the ceramics.
► The depolarization temperature decreases with the increment of A-site vacancy.
► Bi0.505(Na0.82K0.18)0.485TiO3 exhibits high piezoelectric properties.
► Depolarization mechanism is discussed.