Polaronic conduction and spectroscopy of borate glasses containing vanadium

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Abstract
Barium borate glasses containing 0-35 mole% V2O5 were found to be homogeneous. Optical absorption spectra indicated that only V4+ of the lower valence states of vanadium was present. The molar volume data suggested that a change in the structure associated with vanadium ions occurred at around 22% V2O5. ESR spectra showed that a more continuous change occurred in the electron structure associated with the V4+ ions as the V2O5 content was varied. Resistivity and activation energy decreased rapidly with decreasing vanadium-vanadium separation, while, at constant % V2O5, they showed a minimum at V4+/(V4++V5+)=0.45. Thermoelectric power of glasses with 25-30% V2O5 showed very low activation energies, in agreement with a polaron hopping mechanism.