Material softening by cation off-centering in Bi-based lead-free piezoelectric ceramics

The origin of material softening in BiFeO3-BaTiO3 ceramics was assessed by studying the crystal structure and structural parameters. The crystal structure was investigated at 950 K by synchrotron radiation X-ray diffraction using structure refinement; structural parameters were calculated from the final structure refinement results. The crystal structure was cubic, with Bi3+ ions off-centering into six equivalent neighboring sites along the < 100 > direction. We suggested that the stability of the Bi off-centering position and Bi off-centering displacement affects the material softening. The maximum material softening occurred in 0.70BiFeO(3)-0.30BaTiO(3) ceramics with the largest Bi ion off-centering displacement and smallest Bi-O bond length, which provided the stable Bi ion off-centering position. Therefore, the material softening is attributed to the stability of the Bi ion off-centering position and the Bi ion off-centering displacement. The suggested model of material softening can provide essential information for the design and development of next-generation lead-free piezoelectric materials. (C) 2021 The Japan Society of Applied Physics