Electron microscopy analyses and electrical properties of the layered Bi2WO6 phase

The bismuth tungstate Bi2WO6 was synthesized using a classical coprecipitation method followed by a calcination process at different temperatures. The samples were characterized by X-ray diffraction, simultaneous thermogravimetry and differential thermal analysis (TGA/DTA), scanning and transmission electron microscopy (SEM, TEM) analyses. The Rietveld analysis and electron diffraction clearly confirmed the Pca2(1) non centrosymmetric space group previously proposed for this phase. The layers Bi2O22+ and WO42- have been directly evidenced from the HRTEM images. The electrical properties of Bi2WO6 compacted pellets systems were determined from electrical. impedance spectrometry (EIS) and direct current (DC) analyses, under air and argon, between 350 and 700 degrees C. The direct current analyses showed that the conduction observed from EIS analyses was mainly ionic in this temperature range, with a small electronic contribution. Electrical change above the transition temperature of 660 degrees C is observed under air and argon atmospheres. The strong conductivity increase observed under argon is interpreted in terms of formation of additional oxygen vacancies coupled with electron conduction. (c) 2013 Elsevier Inc. All rights reserved.