Thermal and electrical behavior of γ-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-O2. This new synthesis procedure yields to the formation of amorphous powders of 2Bi2O3:V2O5 and Bi2O3:VO2 compositions. Annealing at low temperatures results in the stabilization at room temperature of the high temperature phase γ-Bi2VO5.5 and fluorite-like f-Bi2VO5 not obtained by the traditional solid-state reaction method. Thermal and electrical behavior of these phases has been studied by DTA, XRD with temperature and impedance spectroscopy measurements. Both γ-Bi2VO5.5 and f-Bi2VO5 transform to well-known α-Bi2VO5.5 and α-Bi2VO5, respectively, on heating above 500°C. The conductivity and activation energy values of the phases are characteristic of good ionic conductor materials. The sintering protocol seems to be an essential point to improve their electrical properties.