Synthesis and analysis of lead-free tungsten bronze ferroelectrics

摘要

The polycrystalline Ba_2Sr_3GdTi_3V_7O_(30), a member of tungsten bronze structural family, was prepared by a solid-state reaction method at high temperature (calcination and sintering temperatures at 950 and 1,000 ℃, respectively). Preliminary structural study showed that the compound has orthorhombic crystal structure at room temperature. Study of surface morphology of the compound by scanning electron microscopy exhibits the uniform grain distribution on the surface of the sample with less number of voids. The dielectric anomaly observed at 313 ℃ is considered as a ferroelectric-paraelectric phase transition temperature which has been confirmed by appearance of hysteresis loop at room temperature. The trend of variation of ac conductivity with inverse of absolute temperature provides the nature of conduction mechanism in the material. The different value of activation energy in different temperature regions suggests that the conduction process in the material is of mixed-type (i.e., ionic-polaronic and space charge due to the oxygen ion vacancies).