Thermopower, conductivity and the Hall effect in V₂O₅gels

Abstract

Conductivity, thermoelectric power and Hall effect measurements are reported for V2O5 gels with relative concentrations of V4+ of 0.005 and 0.11. Both the Seebeck and the Hall coefficient are negative. This is an exception to the rule that the sign anomaly effect should be observed for amorphous semiconductors, i.e. that these coefficients should have opposite signs. An irreversible change of conductivity and thermoelectric power with temperature is observed, which is mainly attributed to an irreversible increase of V4+ concentration. The results of thermoelectric power measurements are consistent with a simplified version of the Heikes and Ure formulae for transition-metal oxide glasses.