Defect structure and ionic conductivity as a function of thermal history in BIMGVOX solid electrolytes

The defect structure of the oxide ion conducting solid electrolyte, Mg subs tituted Bi4V2O11-delta (BIMGVOX), was examined by high-resolution powder ne utron diffraction. A detailed explanation of interpretation of the defect s tructure is presented. The general formula for the BIMGVOX solid solutions Bi2V1-xMg(x)O(5.5-3x/2) assumes complete oxidation of vanadium to V-V. Anal ysis of the neutron diffraction data reveals the defect structure and indic ates that there is, in fact, partial reduction of vanadium to V-IV. The ext ent of reduction is dependent on thermal history, with high temperature que nched samples showing a greater degree of reduction than exponentially slow cooled samples. This is correlated with differences in electrical behaviou r at low and high temperatures. Differences in ionic conductivity and activ ation energies between samples with different thermal histories are explain ed in terms of the balance between charge carrier concentration and the ext ent of defect trapping effects. (C) 2001 Kluwer Academic Publishers.