RESUMO
A study of phase and electrical behaviour in the bismuth niobate, Bi(4)NbO(8.5), using x-ray and neutron powder diffraction, thermogravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS) and ac impedance spectroscopy is presented. Two polymorphs were identified in this composition, a tetragonal phase (type III), which can appear at temperatures above 800 °C and a pseudo-cubic phase (type II) evident at lower temperatures. The defect structure analysis of the type II phase is consistent with the existence of chains of niobate polyhedra, which facilitate electronic conduction at low temperatures. The appearance of the type III phase is strongly dependent on experimental conditions and TGA and XPS measurements suggest a likely association with change in oxygen stoichiometry.