Influence of substitution on dielectric and impedance spectroscopy of Sr1-xBi2+yNb2O9 ferroelectric ceramics synthesized by chemical route

Nanocrystalline powders of Sr1-xBi2+yNb2O9 (SBN, x = 0.0, 0.1, 0.2, 0.3, and 0.4; y = 0, 0.066, 0.133, 0.200, and 0.266) were prepared by aqueous solution method using water-soluble Sr-EDTA, Bi-EDTA and Nb-tartarate as the starting materials. XRD showed that the samples were free from fluorite or pyrochlore phase within heat-treatment temperature from 550 to 600 degrees C. Average crystallite size and particle diameter were observed to be between 10 and 25 nm, which were analyzed through XRD and TEM, respectively. Bi-substitution has substantially improved the sinterability of SBN and enabled to achieve high density (96%), which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Sr2+ ions by the trivalent bismuth ions. The complex impedance diagrams of Bi-substituted SBN, x = 0.4 ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for pure and other substituted SBN ceramics show an additional low-frequency semicircle, which was attributed to the blocker size effects. The dielectric behavior of pure and Bi-substituted SBN ceramics was rationalized using the impedance and modulus data. (c) 2007 Elsevier B.V. All rights reserved.