Frequency and temperature dependence of electrical properties of barium and gadolinium substituted SrBi2Nb2O9 ceramics

Barium strontium gadolinium bismuth niobate (Ba0.1Sr0.81Gd0.06Bi2Nb2O9, BSGBN) ceramics were prepared by using the conventional solid-state reaction method. The dielectric permittivity, modulus and impedance spectroscopy studies on BSGBN were investigated in the frequency range, 45 Hz–5 MHz and in the temperature range from room temperature (RT) to 570 °C. The dielectric anomaly with a broad peak was observed at 470 °C. Simultaneous substitution of Ba2+ and Gd3+ increases the transition temperature of SrBi2Nb2O9 (SBN) from 392 to 470 °C. XRD studies in BSGBN revealed an orthorhombic structure with lattice parameters a = 5.4959 A, b/a = 1.000, c = 25.0954 A. Impedance and modulus plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed a non-Debye relaxation. Also, dc and ac conductivity measurements were performed on BSGBN. The electric impedance which describes the dielectric relaxation behaviour is fitted to the Kohlrausch exponential function. Near the phase transition temperature, a stretched exponential parameter β indicating the degree of distribution of the relaxation time has a small value.