Majority charge carrier reversal and its effect on thermal and electron transport in xV2O5–(1 − x) As2O3 glasses

DC resistivity, thermopower and optical absorption of xV2O5–(1 − x) As2O3 (0.58 ≤ x ≤ 0.93) glasses have been studied as a function of composition. The transport mechanism in these glasses has been identified to be a combination of hopping of small polarons between V4+ and V5+ sites and small bipolarons between As3+ and As5+ sites respectively. Electrical conductivity is found to be more of a function of vanadium content than arsenic concentration in the glasses, indicating that the contribution of bipolarons to the conductivity is negligible. Thermopower has also been found to be sensitive to the composition of the glasses. At low vanadium concentrations, the thermopower is negative, which exhibits a sign reversal as vanadium concentration is increased (at x = 0.7). An important feature of these glasses is that the thermopower is not a function of [V5+]/[V4+] ratio, as is normally observed in vanadate glasses, and such a phenomenon suggests that the arsenic ions (bipolarons) in these glasses contribute to the thermal transport phenomena in a significant way.