Simultaneously enhancing piezoelectric performance and thermal depolarization in lead-free (Bi,Na)TiO3-BaTiO3 via introducing oxygen-defect perovskites

For the development of lead-free Bi0.5Na0.5TiO3 prototype materials, it seems conflicting to improve the piezoelectric response (d33) and depolarization temperature (Td) simultaneously. Here, we propose a general chemical substitution method to simultaneously improve d33 and Td of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) via introducing oxygen-defect perovskite. This has been demonstrated by introducing BaAlO2.5 into BNT-BT perovskite crystal lattice and forming solid-solutions, in which a series of ceramics with P4mm phase after electrical poling can be achieved. Not only its d33 but also Td can be much improved, which goes far beyond the performance boundary limit of d33 vs. Td for all BNT-BT based systems. The large d33 stems from the enhancement of lattice strain and domain switching confirmed by in situ synchrotron X-ray diffraction analysis. Critically, the improved Td originates from the increased tetragonality that caused by oxygen vacancies, as elucidated by the comparative experiments and density functional theory calculations. The present study provides a general method to tune the piezoelectric performance of BNT-based ceramics, and expects to benefit other piezoelectric materials.