Increasing the conductivity of V2O5-TeO2 glass by crystallization: structure and charge transfer studies.

In the present paper, V2O5-TeO2 glass was prepared by the melt-quenching technique. Crystallization of glass with a vanadium content higher than 35%mol results in an increase in electrical conductivity by a few orders of magnitude and a decrease in activation energy from ~0.40 to ~0.12 eV. In this work, a critical review of existing charge transfer models was presented on the example of V2O5-TeO2 glass and glass–ceramics. Schnakenberg's and Friedman-Triberis' charge transfer models were found to be applicable to both glass and glass–ceramics. Optical phonon frequencies obtained from Schnakenberg's model are in agreement with FTIR studies. Values of activation energies obtained from the Schnakenberg model decrease after crystallization. Friedman-Triberis' model shows an increase in the density of states near the Fermi level from 1019 eV−1 cm−3 in glass, to 1021 eV−1 cm−3 in glass ceramics. Structural studies show that the main crystallizing phase is Te2V2O9 which occurs with the V2O5 shell in glasses with compositions 50–50%mol and 45–55%mol. It is concluded that crystallization results in the reduction of vanadium ions in the remaining glass matrix which leads to an increase in the V4+/V5+ ratio and therefore, an increase in electrical conductivity. [ABSTRACT FROM AUTHOR]