Relaxation and conduction mechanism of Dy³⁺ substituted SrBi₂Ta₂O₉ ceramics

Dysprosium substituted SrBi₂Ta₂O₉ Aurivillius ceramics with general formula Sr_1−xDy_2x/3Bi₂Ta₂O₉ (x = 0.0, 0.025, 0.05, 0.075, 0.1) are prepared by using the solid state reaction method. X-ray diffraction pattern revealed a single phase orthorhombic (A₂₁am) structure up to x ≤ 0.05 and deleterious phase is obtained for higher concentration. Scanning electron microscope figures show well defined anisotropic grains in all compositions. The electrical relaxation mechanism is studied by the impedance spectroscopy analysis. The Cole–Cole plots are fitted with equivalent circuit and the fitting parameters are presented. The Kohlrausch–Williams–Watts (KWW) function is used to explain the modulus analysis and confirms the coexistence of grain and grain boundary effect. The dispersion of conductivity with frequency is well explained using Jonscher's power law and DC conductivity values are obtained from the fittings. Activation energies are determined from the Arrhenius fitting of impedance and conductivity plots. The determined activation energies give an idea about the reduction of a cluster of vacancies due to the neutralization of oppositely charge vacancies which requires lower energy to mobilize the charge carrier than the individuals.