Polaronic transport properties of some vanadate glasses: effect of alkali-earth oxide modifiers

Abstract

Temperature and composition dependence of the electrical conductivity of alkali-earth vanadate glasses formed with V₂O₅ as a unique glass network former have been investigated in the temperature range 80-500 K. The results for these glasses have been compared with those for the traditional vanadate glasses. The conductivity and the activation energy for the alkali-earth vanadate glasses having V₂O₅ content >70 mol % depend slightly on the nature of the alkali-earth oxide. However, for the glasses with V₂O₅ content >70 mol % the conductivity changes significantly with the nature and the content of alkali-earth oxides. The composition dependence of the electrical properties of the alkali-earth vanadate glasses has been observed stronger than those for the traditional vanadate glasses. The results for the alkali-earth vanadate glasses have been interpreted in terms of polaronic hopping models. The multiphonon assisted hopping model of small polarons in the nonadiabatic regime, which considers the strong interaction of electrons with both the optical and acoustical phonons, is the best to interpret the temperature dependence of the conductivity data of these glasses over the entire temperature range of measurement. The parameters obtained from the fits of the experimental data to this model appear reasonable and are consistent with the glass composition. On the other hand, Mott's optical phonon assisted hopping model at high temperature yields small values for the localization length, while Mott's variable range hopping model is consistent with the low-temperature data only. Schnakenberg's model provided higher values of the hopping and disorder energies than the activation energies obtained at the highest and the lowest temperature ranges, respectively. The addition of the alkali-earth oxide modifiers to the vanadate network alters the hopping mechanism from adiabatic to nonadiabatic.