Local structure and conductivity of highly conductive vanadate glasses containing different metal oxides

Abstract

Heat treatment of 20BaO·xMmOn·(10−x)Fe2O3·70V2O5 glasses containing different metal oxides (MmOn), such as Fe2O3, Al2O3, MnO2, CuO, Cu2O, ZnO, Ga2O3, GeO2, MoO3, SnO2 and WO3, was accompanied by a remarkable decrease in DC-resistivity (ρ) at room temperature from the order of MΩ cm to Ω cm. N-type semiconductor model could be successfully applied to discuss the conduction mechanism. Introduction of CuO into network former (NWF) sites caused a remarkable change of ρ from 2.6 × 105 to 3.1 Ω cm when annealed at 450 °C for 30 min. Activation energy for conduction (Ea) decreased from 0.16 to 0.10 eV, suggesting an increased carrier density in the conduction band. Diffuse reflectance spectra of this glass showed a decrease in the bandgap energy (Eg) from 2.41 to 2.14 eV. Introduction of ZnO into network modifier (NWM) sites resulted in a remarkable decrease in ρ from 4.0 × 105 to 4.8 Ω cm after annealing at 450 °C for 30 min, together with a decrease in Ea from 0.23 to 0.14 eV. Diffuse reflectance spectra showed a decrease in Eg from 2.39 to 2.11 eV. These results prove that heat treatment of vanadate glass causes structural relaxation and concordant decrease in Ea and Eg which are responsible for the remarkable increase in the high conductivity.