A-site vacancy-induced giant strain and the electrical properties in non-stoichiometric ceramics Bi0.5+x(Na1−yKy)0.5−3xTiO3

A-site vacancies were created in lead-free piezoelectric non-stoichiometric ceramics Bi0.5+x (Na1−yKy)0.5−3xTiO3 and Bi0.5+x (Na0.82K0.18)0.5TiO3, which were synthesized by a conventional solid-state reaction process. The ferroelectric properties, piezoelectric performances and strain behaviours of the as-prepared ceramics were characterized, and the effects of A-site vacancies on the ferroelectric properties, piezoelectric performances and strain behaviours of the ceramics were discussed. The results show that moderate A-site vacancies in the prepared ceramics enhance the piezoelectric performance of the ceramics, meanwhile, A-site vacancies lead to a decrement of depolarization temperature Td. A large bipolar strain of 0.35% is achieved in the Bi0.505(Na0.74K0.26)0.485TiO3 ceramic at room temperature.