Semiconducting properties of V₂O₅ gels

Abstract

Mixed-valence vanadium pentoxide gels have been obtained by polymerization of vanadic acid. They exhibit semiconducting properties which arise from electron hopping between V^IV and V^v ions. Such gels can easily be deposited onto a substrate, giving layers of high electrical conductivity (σ =0.l Ω⁻¹ cm⁻¹ at 300 K). Their electrical properties can be described by the small-polaron model, and the main parameters have been determined by conductivity measurements, E.S.B. and optical spectroscopy. The optical and thermal activation energies are found to be E _opt = 0.87 eV and E_th = 0.17eV. The transfer integral J = 0 05 eV is quite small, and the electron–phonon coupling parameter γ = 14 is rather high. The structural disorder of this amorphous semiconductor was estimated from electrical and E.S.R. experiments. It leads to a localization of the charge carriers.