Complex impedance studies of tungsten–bronze structured Ba5SmTi3Nb7O30 ferroelectric ceramics

This paper reports complex impedance analysis of polycrystalline tungsten–bronze structured Ba5SmTi3Nb7O30 prepared by a solid-state reaction method. X-ray diffractogram analysis reveals the formation of the compound in an orthorhombic crystal system. Scanning electron microscopy has been used to investigate the grain morphology of the material. Variation of dielectric constant (εr′) with temperature at different frequencies shows that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 170  ∘C, and exhibits diffuse phase transition. Impedance plots have been used as a tool to analyse the electrical characteristics of the sample as a function of frequency and temperature. Bulk resistance is observed to decrease with an increase in temperature, showing a typical negative temperature coefficient of resistance (NTCR) type behaviour. Nyquist or Cole–Cole plots show the existence of both grain and grain boundary effects only at a high temperature (375  ∘C). Relaxation time is found to decrease with a rise in temperature and it obeys the Arrhenius relationship. The corresponding activation energy is found to be about 0.95 eV. Variation of dc conductivity as a function of temperature has also been studied.