Frequency-dependent dielectric characteristics of ferroelectric SrBi2Nb2O9 ceramics

The dielectric properties of ferroelectric SrBi2Nb2O9 (SBN) ceramics have been studied in the frequency range of 100 Hz to 1 MHz at various temperatures (300–823 K). A strong low frequency dielectric dispersion (LFDD) is encountered in these ceramics in the 573–823 K temperature range. Electrical conductivity data indicate that the conductivity in SBN is essentially due to oxygen vacancies and the activation energy for the conduction in the high temperature region is found to be 0.90 eV. The dielectric constants measured as a function of frequency (100 Hz–1 MHz) in the 300–823 K temperature range have been found to fit to the Jonscherʹs dielectric dispersion relations: εr′=ε∞+sin(n(T)π/2)ωn(T)−1a(T)/εo and εr″=σ/εoω+cos(n(T)π/2)ωn(T)−1a(T)/εo. The high frequency (1 MHz) dielectric constant (ε∞) shows a peak at Tc (723 K).The coefficient A(T) (=a(T)S/L) and the exponent n(T) of the Jonscherʹs expression are determined. The exponent n(T) is found to be minimum at the Curie temperature, Tc. The parameter A(T), which indicates the strength of the polarizability, shows a prominent peak in the vicinity of the Curie temperature.