Dynamics of the phase transition in Bi0.5Na0.5TiO3 based on in situ Raman spectroscopy

Abstract

This work aims to provide a thorough analysis of the phase transition dynamics in lead-free Bi_0.5Na_0.5TiO₃ by in situ Raman spectroscopy, which is conducted under varying temperature and electric field. All the transition points are proved by the Raman response of phonon vibration, including the depolarization temperature at ∼200 °C, potential transition at ∼280 °C, Curie temperature at ∼320 °C and tetragonal-cubic transition above ∼500 °C. The vibration of A-site ions primarily contributes to the depolarization behavior, which is also responsible for the strong polarity in Bi_0.5Na_0.5TiO₃. The transitions at ∼280 °C and ∼320 °C are confirmed by the phonon vibrations of the Ti–O bonds and the TiO₆ octahedra. Meanwhile, the distortion of the Ti–O bonds and TiO₆ octahedra under an electric field results in weak polarity. The thermal hysteresis behavior is related to the dynamics of phonon thermal evolution, because of the delayed response of the vibration mode to thermal activation of Ti–O bonds and TiO₆ octahedra. The results lay a foundation for understanding the mechanism of the phase transition and polarization in Bi_0.5Na_0.5TiO₃, guiding the design of functional devices for electromechanical applications.