Polarization Rotation at Morphotropic Phase Boundary in New Lead-Free Na_1/2Bi_1/2V_1-xTi _xO₃ Piezoceramics

In this work, we show that polarization rotation enhances the piezoresponse in a high-performance lead-free piezoelectric material, Na1/2Bi1/2V1-xTixO3, a solid solution between tetragonal Na1/2Bi1/2VO3 and rhombohedral Na1/2Bi1/2TiO3, obtained by high-pressure synthesis. The system forms a pure perovskite structure with a favorable morphotropic phase boundary (MPB) located around x = 0.90, which separates the tetragonal and rhombohedral phases. In addition, a distinct monoclinic phase with polarization rotation as functions of composition and temperature is observed. XRD measurements revealed the moderately high Curie temperature of 523 K at x = 0.95 in the MPB. The piezoelectric coefficient d33 of the monoclinic x = 0.95 sample, 42 pC/N, is higher than those of the tetragonal and rhombohedral phases. Even though the present lead-free Na1/2Bi1/2V1-xTixO3 ceramics feature smaller d33 values compared to many currently available lead-free piezoelectric materials as a result of insufficient poling and low density, we expect our findings open up opportunities for exploring promising lead-free piezoelectric materials in Na1/2Bi1/2VO3-based perovskites.