Large strain lead-free ceramic materials for actuators

In this paper we present a set of (Bi_0.5Na_0.5)TiO₃-based lead-free ceramics which can provide large strain in response to an external electric field. An effective piezoelectric constant, S_max/E_max, as high as 830 pm/V, is obtained in optimized compositions under proper exciting conditions. This value is comparable to some soft PZT ceramics used in modern multilayer actuators. Electromechanical measurements suggest that the large strain mainly arises from 1), the high electrostrictive contribution of a non-polar phase and 2), a field induced phase transition accompanied by a volume change. The temperature and frequency dependences of the electromechanical response are presented and discussed from the point of view of phase transition dynamics. The implementation of these non-piezoelectric effects and related ceramics for actuator applications is discussed based on the material properties and practical requirements.