DC conduvtivity of V 2O 5TeO 2 glasses

Abstract

The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V 2O 5 has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V 2O 5 content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v 0. Adiabatic hopping is indicated for v 0∼10 11 Hz, however this value leads to unreasonably low value for the Debye temperature θ D, and higher values for v 0∼10 13 hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V 2O 5TeO 2 glasses. The low temperature data (< 100 K) can be fitted to Mott's variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy.