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

Abstract In order to create A-site vacancy in lead-free piezoelectric ceramics Bi 0.5 (Na 0.82 K 0.18 ) 0.5 TiO 3 , non-stoichiometric ceramics Bi 0.5+ x (Na 0.82 K 0.18 ) 0.5−3 x TiO 3 and Bi 0.5+ y (Na 0.82 K 0.18 ) 0.5 TiO 3 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. Bi 0.505 (Na 0.82 K 0.18 ) 0.485 TiO 3 ceramic possesses the highest piezoelectric properties and strongest ferroelectricity: piezoelectric coefficient d 33  = 151 pC/N; electromechanical coupling factor k p  = 29.8%; mechanical quality factor Q m  = 124; remnant polarization P r  = 29.5 μC/cm 2 ; coercive field E c  = 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 T d .