Domain evolution and coercive field reduction in rhombohedral (Na0.5Bi0.5)TiO3-based crystals by alternating electric field

Abstract

(Na0.5Bi0.5)TiO3 (NBT)-based materials have been widely studied for their large electric-field-induced strains. However, a high coercive field (Ec) has long hindered the applications of NBT-based materials. Here, we propose a simple method to significantly reduce the Ec of rhombohedral NBT-based crystals through domain engineering. By applying an alternating current (AC) electric field along the [001] direction, the Ec of Mn-doped (Na0.485K0.015Bi0.5)TiO3 single crystal can be reduced from 70 to 20 kV/cm after about 25 cycles without sacrificing the ferroelectric polarization. Meanwhile, the piezoelectric coefficient d33 and the optical transparency of the crystals are also enhanced compared with those after direct-current electric field poling. The domain structure characterization shows that the AC cycles can form a laminar domain configuration, in which the 109° domain walls are parallel to (001) planes. It is demonstrated that in the laminar domain configuration, almost only 71° polarization switching occurs when the external electric field is reversed. The required energy for polarization reversal is significantly lower than that of the “4R” domain configuration; thus, the Ec is reduced greatly. The low Ec is maintained after depolarization at 250 °C, evidencing good thermal stability of the laminar domain configuration. Furthermore, this method is also applicable to other rhombohedral single crystals and may be applied to [001]-textured polycrystalline ceramics in the future; thus, it may indeed benefit the practical applications of NBT-based piezoelectric devices.