Anomalous dielectric behavior of poled K0.5Bi0.5TiO3 ceramics

Abstract

Perovskite K0.5Bi0.5TiO3 (KBT) ceramics were prepared via the solid-state synthesis method and the structural, dielectric, and piezoelectric properties in unpoled & poled states were analyzed to resolve the reported discrepancies in this material. The Rietveld refinement of room-temperature x-ray diffraction data of the unpoled KBT shows the coexistence of tetragonal (P4mm) & cubic (Pm3‾m) phases. However, two tetragonal phases (P4mm) with different c/a ratios were suggested in poled KBT, signifying the external electric field effect on structural transformation. These structural changes were further corroborated by the appearance of an additional anomaly in the temperature-dependent dielectric permittivity of poled KBT ceramic. The possible mechanisms responsible for electric field-dependent phase transformation and anomalous dielectric behavior of KBT ceramics are discussed. The temperatures of normal to relaxor ferroelectric transition (TF-R) and depolarization (Td) were estimated to be ∼280 °C and 320 °C, respectively. The higher value of Td than TF-R implies the nonergodic relaxor state in KBT ceramic. Dielectric and piezoelectric measurements performed on relaxor ferroelectric BiAlO3 modified KBT ceramics further strengthen the proposed mechanisms responsible for anomalous dielectric behavior in poled KBT ceramics. © 2021 Elsevier Ltd and Techna Group S.r.l.