Identifying the Opposite Shift Behavior between Depolarization and Relaxation in BNT-Based Ceramics

As a kind of classical ferroelectric material with perovskite structure, the intricate phase transition in Bi_0.5Na_0.5TiO₃ (BNT) has been of increasing interest in dielectric physics. In particular, the transition from rhombohedral to rhombohedral/tetragonal coexistence occurring at ∼200 °C is usually accompanied by depolarization and relaxation. Thus, these two polarization phenomena are generally attributed to the phase transition by previous reports, simplistically. In this work, the experimental results including dielectric, in situ piezoelectric, and pyroelectric properties indicate the different temperatures between depolarization and relaxation in BNT. Moreover, Cr and Mo cations are introduced in B-sites of BNT with different ionic radii, which further exerts noteworthy regulatory effect on the opposite temperature shift between depolarization and relaxation properties. Finally, the in situ Raman spectra with varying temperatures provide a detailed insight into the mechanism of depolarization and dielectric relaxation from the perspective of the evolution of phonon vibration. These findings hold important significance for guiding the design and property regulation of BNT-based dielectric materials.