Influence of Bi-site Substitution on the Ferroelectricity of the Aurivillius Compound Bi₂SrNb₂O₉

Abstract

Ceramics based on the composition Bi₂SrNb₂O₉ with isomorphic substitutions of cations in the Bi₂O₂²⁺ and the perovskite layers, Bi_2−xTe_xSr_1−xNa(K)_xNb₂O₉, have been prepared by solid state reaction. The ferroelectricity of this Aurivillius type structure has been studied. Dielectric measurements as a function of the temperature show a low temperature maximum in the dielectric constant that would correspond to a ferro-;paraelectric phase transition. The temperature of this maximum increases when the radius of the ion that substitutes Sr for decreases. A second maximum in the dielectric constant is found at higher temperature possibly corresponding to a relaxor ferroelectric. Measurements of remanent polarization as a function of the temperature seem to confirm the relaxor behavior, because the polarization disappears at temperatures between the two maxima of the dielectric constant. Saturated hysteresis loops are obtained for all the substituted samples at temperatures above 300 °C. Ferroelectric parameters such as the polarization, coercive field, and coupling factors of the BSN family compounds were obtained for the first time. The ac electric conductivity shows anomalies at temperatures close to those where the remanent polarization disappears. Activation energies calculated from measurements of dc electric conductivity, impedance arcs, and dielectric modulus data may be associated with thermally activated oxygen vacancies.