NaTaO3-driven structural frustration at the rhombohedral/monoclinic crossover of Na0.5Bi0.5TiO3–BaTiO3 piezoceramic resulting enhanced properties

Abstract

The morphotropic phase boundary (MPB) in Na_0.5Bi_0.5TiO₃–BaTiO₃(NBT–BT) piezoelectrics is often modified to enhance functional properties; however, the structural crossover between rhombohedral and monoclinic phases at low BaTiO₃ (BT) content remains underexplored. In this study, we investigate the impact of NaTaO₃ (NT) doping on the structural and functional properties of NBT-BT near the low BT crossover. Temperature-dependent X-ray diffraction, dielectric, pyroelectric, and microstructural analyses reveal that NT doping promotes non-ferroelectric lattice distortions, breaking long range ferroelectric order and enhancing multifunctional behaviour. NT-modified compositions demonstrate large electrostrain, improved weak-field piezoelectric coefficients, and high recoverable energy density under low electric fields. Importantly, the depolarization temperature is found to be unrelated to a structural phase transition, challenging conventional understanding. A detailed composition–temperature (x–T) phase diagram is established, identifying new phase boundaries and clarifying structure–property relationships. These findings offer valuable insights into compositional tuning strategies for improving the thermal and functional stability of lead-free piezoelectric materials.