Low temperature dc electrical conductivity of V2O5-SnO-TeO2 glasses exhibiting majority charge carrier reversal

The dc electrical conduction in xV2O5.20SnO . (80 - x)TeO2 (18 mol% less than or equal to x less than or equal to 50 mol%) glasses has been studied in the temperature range from 100 to 480 K. Glasses with x less than or equal to 20 exhibited p-type conduction whereas the rest show n-type conduction. All the glass compositions exhibited a crossover from variable range hopping (VRH) to small polaron hopping (SPH) conduction at a characteristic temperature well below room temperature. The low temperature dc conduction mechanism in these glasses has been analysed using Mott's approach. Mott parameter analysis gave values for the density of states at the Fermi level N(E-F) between 1.42 x 10(26) m(-3) eV(-1) and 15.0 x 10(21) m(-1) eV(-1) at 230 K. The disorder energy W-d was found to be varying between 0.02 and 0.03 eV. N(E-F), the average hopping distance R-VRH and the VRH-SPH transition temperature T-R exhibit an interesting composition dependence, which is interpreted in terms of the majority charge carrier reversal (MCCR) phenomenon occurring in these glasses.