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 θ_D/2 (θ_D: the Debye temperature); the electrical conduction at T>θ_D/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 θ_D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.