Characterization and Conduction Mechanism of Highly Conductive Vanadate Glass

This paper reviews recent studies of highly conductive barium iron vanadate glass with a composition of 20 BaO center dot 10 Fe2O3 center dot 70 V2O5 (in mol %). Isothermal annealing of the vanadate glass for several ten minutes at a given temperature, higher than glass transition temperature or crystallization temperature, caused an increase in o. Substitution of Cu-I (3d(10)), Zn-II (3d(10)) and Cu-II (3d(9)) for Fe-III (3d(5)) was investigated to elucidate the effect of electron configuration on the conductivity (sigma). A marked decrease in the activation energy of conduction (E-a) was also observed after the annealing. Values of E-a were correlated to the energy gap between the donor level and the conduction band (CB) in the n-type semiconductor model. Isothermal annealing of Zn-II-substituted vanadate glass (20 BaO center dot 5 ZnO center dot 5 Fe2O3 center dot 70 V2O5) at 450 degrees C for 30 mm showed an increase in cr from 2.5 x 10(-6) to 2 1 x 10(-1) S cm(-1), which was one order of magnitude larger than that of non-substituted vanadate glass (3.4 x 10(-2) S cm(-1)). Under the same annealing condition, a's of 2.0 x 10(-1) and 3.2 x 10(-1) S cm(-2) were observed for 20 BaO center dot 5 Cu2O center dot 5 Fe2O3 center dot 70 V2O5 and 20 BaO center dot 5 CuO center dot 5 Fe2O3 center dot 70 V2O5 glasses, respectively. These results demonstrate an increase in the carrier (electron) density in the CB, primarily composed of anti-bonding 4s-orbitals.