Anomalous temperature variation of thermoelectric power in CdO and Ag2O substituted lead vanadate glass system

Thermoelectric power studies on eutectic lead vanadate glass system in which CdO or Ag2O is substituted for PbO upto 15 mol% are reported in the temperature range 300-500 K. It was observed that while the un-substituted samples exhibit almost temperature-independent thermoelectric power, the CdO and Ag2O substituted samples exhibit thermoelectric power with marked temperature dependence. The Ag2O substituted samples remain n-type with an increase in the magnitude of thermoelectric power while the CdO substituted samples exhibit a change from n- to p-type as the temperature is increased. Application of Emin's formula gives a reasonable estimate of the disorder energy (W D) for Ag2O substituted samples, while for CdO substituted samples the W D values obtained are supposed to be too large to be acceptable. These observations are discussed in the light of recently reported results on similar systems