Nature of the Dielectric Anomaly in Na_0.5Bi_0.5TiO₃-Based Ferrolectrics

The temperature-frequency dependence of dielectric permittivity in Na_0.5Bi_0.5TiO₃ (NBT) -based compositions displays a diffused, frequency-independent maximum along with a frequency-dependent shoulder below this maximum. This behavior deviates from that of both classical ferroelectrics and conventional relaxor ferroelectrics, and its interpretation is further complicated by challenges in linking it to known structural phase transitions. This study proposes a new interpretation of the dielectric behavior of NBT-based materials through a comparative analysis of temperature-frequency permittivity data in both unpoled and poled NBT samples and 0.95Na_0.5Bi_0.5TiO₃-0.05CaTiO₃ solid solution over a broad frequency range (10 Hz-100 MHz). Results reveal that the steep permittivity change between the maximum and shoulder-accompanied by pronounced thermal hysteresis-can be attributed to a phase transition between two non-ferroelectric phases. When this contribution is excluded, the dielectric response aligns with classical relaxor ferroelectric behavior. To reconcile this with other known properties of NBT, the "breathing" model is employed, offering a unified framework for understanding its relaxor-like characteristics.