Material softening by cation off-centering in Bi-based lead-free piezoelectric ceramics
Sangwook Kim, Hyunwook Nam, Ichiro Fujii, Shintaro Ueno, Chikako Moriyoshi, Yoshihiro Kuroiwa, Satoshi Wada
Abstract
Abstract The origin of material softening in BiFeO 3 –BaTiO 3 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 Bi 3+ 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.