Structural, dielectric and electrical studies in tungsten doped SrBi_2Ta_2O_9 ferroelectric ceramics

摘要

The effect of tungsten doping on the structural, dielectric and impedance properties of SrBi_2Ta_2O_9 (SBT) ferroelectric ceramics is reported. Tungsten doped SrBi_2(W_xTa_(1-x))_2O_9 (0.0 < = x < = 0.20) ceramics were synthesized by the solid state reaction method. X-ray diffractograms of the samples reveal the single phase layered perovskite structure formation with tungsten content x < = 0.05. Variation in the lattice parameters has been explained in terms of the limited structural constraint and relaxation imposed by the Bi-0 interlayer. Dielectric constant (e) and dielectric loss (tan S) measurements as a function of temperature reveal a decrease in the Curie temperature (T_c) from 320 deg C (for x = 0.0) to 291 deg C (for x = 0.025) and an increasing trend over the doping range of 0.05 < = x < = 0.20. Significant reduction in the dielectric loss with tungsten addition have been observed. The observed changes in e and tan 5 with frequency and temperature have been considered in the light of oxygen and cationic vacancies in tungsten doped samples. Dielectric constant of the samples increases with tungsten doping at their respective Curie temperatures. These have been viewed in terms of relative dominance of the ionic and electronic polarizations. Bulk conductivity of the samples as deduced through ac impedance investigations indicate an increased electronic conduction beyond the observed solubility limit of 0.05 of tungsten doping.