Structure and electrical properties of vanadium boro-phosphate glasses

In this paper, we have studied structure and electrical conductivity of 0.5V2O5-0.5[xB2O3-(1 − x) P2O5] glasses. The reduced vanadium ion ratio V4 +/(V4 + + V5 +) and the ratio of bridging oxygens to non-bridging oxygens have been determined from analysis of V2p3/2 and O1s X-ray photoelectron spectra respectively. It is observed that the reduced vanadium ion ratio V4 +/(V4 + + V5 +) decreases continuously with the substitution of P2O5 by B2O3. The dc conductivity shows a minimum for composition x = 0.4. The electrical conductivity data has been analyzed with various models existing in literature. It is observed that at high temperatures Mott's nearest neighbor hopping model can explain the dc conductivity data, while at low temperatures dc conductivity data is consistent with Mott's variable range hopping model. Schnakenberg's polaron hopping model is valid for the entire temperature range of measurement. The parameters obtained from these models are reasonable.