Thermopower of Semiconducting Glasses in the V2O5-P2O5 and V2O5-CdS-P2O5 Systems

Vanadium phosphate and cadmium sulfide-doped vanadium phosphate glasses containing up to 50–80 mol % V2O5 are prepared. The thermopower of these glasses is measured in the temperature range 303–473 K. The activation energies are determined from the linear dependences of the thermopower S and the logarithm of the conductivity logσ on the reciprocal of the temperature 1/T. It is demonstrated that the activation energies obtained by two methods differ from each other. The difference between the activation energies is referred to as the hopping energy Δ. The possibility of an Anderson metal-insulator transition occurring is examined. It is revealed that similar transitions are not observed in the glasses under investigation. The data obtained are analyzed within the small-polaron hopping model describing the electron conduction. It is established that hopping conduction proceeds over localized states in the tail of the density of states. All the glasses are characterized by electron conduction.