Field-induced phase transition in Bi1/2Na1/2TiO3-based lead-free piezoelectric ceramics

The origin of the electric field-induced strain in the polycrystalline ceramic 0.92Bi1/2Na1/2TiO3-0.06BaTiO3-0.02K1/2Na1/2NbO3 was investigated using in situ high-resolution X-ray and neutron diffraction techniques. The initially existing tetragonal phase with pseudocubic lattice undergoes a reversible phase transition to a significantly distorted rhombohedral phase under electric field, accompanied by a change in the oxygen octahedral tilting from a0a0c+ to a-a-a- and in the tilting angle. The polarization values for the tetragonal and rhombohedral phases were calculated based on the structural information from Rietveld refinements. The large recoverable electric field-induced strain is a consequence of a reversible electric field-induced phase transition from an almost nonpolar tetragonal phase to a ferroelectrically active rhombohedral phase. (orig.)