Non-linear concentration-dependent electrical properties of some semiconducting vanadate glasses

Abstract

Characterizations of (50 − x) P2O5-x M-50V2O5 (M = Bi2O3, Sb2O3, and GeO2 and x=0 to 45 mol% M) and P2O5-Bi2O3 semiconducting oxide glasses have been made from studies of electrical conductivities (both a.c. and d.c.) in the temperature range 77 to 400 K. All these glasses showed some interesting non-linear variation of d.c. and a.c. conductivity, together with other properties for particular values of M (between 20 and 30 mol% M). Because the non-vanadate (1−x) P2O5-x Bi2O3 glasses also showed similar conductivity anomaly (minimum) around 25 mol% Bi2O3 with a corresponding maximum in the activation energy (W), it is concluded (in contradiction to earlier suggestions) that not only the ratio β (= V5+/V4+) but also the network-former ions in the vanadate glasses make a substantial contribution to the anomalous concentration variation of the physical properties of these glasses. The electrical conduction in these glasses is found to be mainly due to hopping of polarons in the adiabatic approximation. At low temperature, the d.c. conductivity obeys Mott's T−1/4 behaviour. The a.c. conductivity obeying the general ωs law (exponent s lying between 0.85 and 0.98) supports the theory based on the hopping over the barrier model.