Anomalous DC electrical conductivity in mixed transition metal ions doped borate glasses

A novel series of borate glasses in the composition, xCo3O4 + (50 − x) (V2O5) + 50 B2O3 where x = 0.05 to 0.45 have been prepared by melt quenching technique. X-ray diffraction studies confirmed the non-crystalline nature of the samples. The room temperature density and molar volume varied non-linearly with cobalt concentration. Electrical conductivity and activation energy were determined and both varied non-linearly with cobalt concentration. Conductivity reached minimum and activation energy reached maximum at x = 0.4 of cobalt concentration. This anomalous behavior is due to the enhancement of Anderson localization caused by increase in configurational disorder. Various polaron related parameters were investigated in the light of Mott's SPH model for T>θD2. The density of states at fermi level was determined using Greaves VRH model which adequately explains conductivity for T<θD2. The nonlinear variation in various physical parameters with second TMI is attributed to the mixed transition effect.