Field-induced phase transition in Bi_1/2Na_1/2TiO₃-based lead-free piezoelectric ceramics

Abstract

The origin of the electric field-induced strain in the polycrystalline ceramic 0.92Bi 1/2 Na 1/2 TiO 3 –0.06BaTiO 3 –0.02K 1/2 Na 1/2 NbO 3 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 a 0 a 0 c + 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.