Polaronic conduction and spectroscopy of borate glasses containing vanadium

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.