The role of V2O5 in the modification of structural, optical and electrical properties of vanadium barium borate glasses

Vanadium barium borate glasses were prepared by a normal melt quench technique. The infrared spectra of these V2O5·BaO·B2O3 glasses were recorded over a continuous spectral range (400-4000 cm−1) in an attempt to study their structure systematically. The conversion from three- to four-fold coordinated boron took place. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of the absorption edge and hence the value of the optical band gap was found to depend on the semiconducting glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of the Urbach energy is associated with phonon-assisted indirect transitions. The theoretical optical basicity has been calculated and is correlated with a change in the optical band gap. The variation in density and molar volume with composition has been investigated in terms of the structural modifications that take place in the glass matrix on addition of V2O5. The DC electrical conductivity as function of the V2O5:BaO and the V2O5:B2O3 ratio has been measured. The change in conductivity and activation energy with composition indicates that the conduction process varies from ionic to polaronic.