Phase transition and failure at high temperature of bismuth-layered piezoelectric ceramics

High-temperature bismuth-layered piezoelectric ceramics (CaxSr1-x)Bi4Ti4O15have been prepared by the conventional solid reaction method. Our results reveal that there is a "phase transition induced by the composition" taking place in the solid solution at around x=0.4. During transition, the crystal structure changes from orthorhombic to pseudo-tetragonal and then back to orthorhombic. Although all (CaxSr1-x)Bi4Ti4O15(with any x value) undergo a second-order ferroelectric-to- ferroelectric phase transition at about 200°C below their Curie temperature, only the ceramic with x=0.4 exhibits a failure in piezoelectric properties during the transition. It is suggested that, on the basis of the X-ray photoelectron spectroscopy results, this material failure is induced by the high concentration of oxygen vacancies in the material during the phase transition.