Thermal and electrical behavior of gamma-Bi2VO5.5 and f-Bi2VO5 oxides obtained from mechanochemically activated precursors

The mechanochemical activation method has been used in order to reduce the synthesis times and temperatures for oxides in the system Bi-V-O-2. This ne w synthesis procedure yields to the formation of amorphous powders of 2Bi(2 )O(3):V2O5 and Bi2O3:VO2 compositions. Annealing at low temperatures result s in the stabilization at room temperature of the high temperature phase ga mma -Bi2VO5.5 and fluorite-like f-Bi2VO5 not obtained by the traditional so lid-state reaction method. Thermal and electrical behavior of these phases has been studied by DTA, XRD with temperature and impedance spectroscopy me asurements. Both gamma -Bi2VO5.5 and f-Bi2VO5 transform to well-known alpha -Bi2VO5.5 and alpha -Bi2VO5, respectively, on heating above 500 degreesC. The conductivity and activation energy values of the phases are characteris tic of good ionic conductor materials. The sintering protocol seems to be a n essential point to improve their electrical properties. (C) 2001 Elsevier Science Ltd. All rights reserved.