Polarization mechanism in filled tungsten bronze Ba4Sm2Ti4Nb6O30 with pinched P–E hysteresis loops

Abstract

Ferroelectric transition and polarization characteristics were explored for filled tungsten bronze Ba4Sm2Ti4Nb6O30 ceramics with pinched P–E hysteresis loops. Two dielectric permittivity peaks were observed at around 553 and 486 K on heating and cooling cycles, respectively, with a large thermal hysteresis (∼77 K), indicating the first-order ferroelectric phase transition behavior in the present ceramics. In addition, a low-temperature dielectric relaxation appeared at around 300 K, following the Vogel–Fulcher relationship, which is related to thermal activation related to the polarization in the ab plane. Pinched P–E hysteresis loops were detected in the temperature range of 293–453 K with two pairs of coercive fields, indicating certain polar reversal mechanism, while E1 corresponds to the reversal field needed for all the ferroelectric domains in the system, and E2 is the back switch field from the polar state to the nonpolar state. Therefore, (E1–E2)/2 is the effect coercive field for the polar domain induced by the field transition. Temperature dependence of the coercive fields E1, E2, and (E1–E2)/2 is fitted to the Vopsaroiu model with different activated energies obtained for different temperature ranges, based on which the polarization dynamics of the pinched hysteresis loops are discussed.