Origin of large electric-field-induced strain in pseudo-cubic BiFeO3-BaTiO3 ceramics

High-performance lead-free piezoelectric materials are in great demand for actuator applications replacing the mainstay Pb(Zr, Ti)O-3 materials. In this research, pseudo-cubic 0.64BiFeO(3)-0.36BaTiO(3) (0.64BF-0.36BT) lead-free ceramics were studied, exhibiting high electric-field-induced strain of 0.38% (60 kV/cm) with large signal piezoelectric coefficient d(33)* of 720 pm/V (40 kV/cm) and low strain hysteresis of 8% at 150 degrees C. It is important that the strain (40 kV/cm) of prototypic co-fired multilayer actuator is found to increase from 0.22% to 0.3% at elevated temperature of 150 degrees C, accompanied by a significantly decreased strain hysteresis. The behind mechanism of the large unipolar strain was investigated by in-situ synchrotron powder X-ray diffraction under different electric fields, being analogous to (Bi, Na)TiO3-BaTiO3 based ceramics but different from Pb(Zr,Ti)O-3 based counterparts. An evident transition from pseudocubic to rhombohedral phase was triggered above electric field of 10 kV/cm, where the lattice distortion, domain switching and phase transition synergistically contribute to the observed large macrostrain. These results demonstrate that the lead-free BiFeO3-BaTiO3 ferroelectric ceramics with pseudo-cubic phase have great potential for high temperature actuator applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.