Site occupancy and electric-field induced strain response of Er-doped (Bi0.4Na0.4Sr0.2)TiO3 ceramics

Er-doped (Bi0.4Na0.4Sr0.2)TiO3 powders were prepared by solid state reactions according to A-site donor (Bi0.4-x/3Na0.4-x/3Sr0.2-x/3Erx)TiO3 (x = 0.0.015 and 0.02) and B-site acceptor (Bi0.4Na0.4Sr0.2)Ti1-yEryO3 (y = 0, 0.015 and 0.02) substitutional doping mechanisms. In both cases, room-temperature X-ray diffraction analyses revealed a decrease of the unit cell volume with increasing Er contents, suggesting A-site occupancy to be thermodynamically more favourable. Over the 25–175 °C temperature range, A-site doped ceramics, in particular x = 0.015, showed enhanced thermal stability of the maximum achievable electric-field induced strain. Importantly, this minor doping level also reduced dielectric loss at high temperature and led to a transition from non-ergodic to ergodic relaxor behaviour. These results may further motivate the study of the impact of other minor dopants in this family of Pb-free piezoceramics. •Er preferential A-site occupancy in BNT-20ST perovskite-based ceramics.•Er doping leads to a transition from non-ergodic to ergodic relaxor behaviour.•Er enhances electrostrain and its temperature stability in BNT-20ST ceramics.