Small polaron transport in V2O5–NiO–TeO2 glasses

Abstract

Semiconducting glasses of the V2O5–NiO–TeO2 system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10−7 to 10−1 S m−1, indicating that the conductivity increased with increasing V2O5 concentration. A glass of composition 67.5V2O5–2.5NiO–30TeO2 (mol %) having a conductivity of 2.47×10−2 S m−1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above θD/2 (θD: the Debye temperature); the electrical conduction at T>θD/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10−7 to 5.48×10−5 cm2 V−1 s−1 at 400 K. The carrier density is evaluated to be 1.85×1019–5.50×1019 cm−3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below θD/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.