Small polaron hopping conduction in V2O5–Sb–TeO2 glasses

The dc electrical conductivity of glasses in the system V2O5–Sb–TeO2 prepared by press quenching was studied at temperatures between 303 and 473 K. The composition range of the glass formation region was found to be 10⩽TeO2⩽100 mol%, 0⩽V2O5⩽70 mol%, and 0⩽Sb⩽20 mol%, respectively. The glasses indicated n-type semiconductors from the measurement of thermoelectric power. The dc conductivities at 473 K for the present glasses were determined to be 6.38×10−6–7.13×10−3 S cm −1, indicating that the conductivity increased with increasing V2O5 concentration. Sb content also contributed to increase the conductivity and decrease activation energy for electrical conduction. A model of redox reaction during melting was proposed and quantitatively explained the reaction between V2O5 and Sb. A glass of composition 70V2O5 · 20Sb · 10TeO2 (mol%) having a conductivity of 7.13×10−3 S cm −1 at 473 K was found to be the highest conductive glass among the previous vanadium–tellurite glasses. From the conductivity-temperature relation, it was found that small polaron hopping model was applicable at the temperature above 12ΘD (ΘD : the Debye temperature); the electrical conduction at T>12ΘD was due to adiabatic small polaron hopping of electrons between vanadium ions for V2O5⩾50 mol%, and non-adiabatic for 30⩽V2O5<50 mol%. The polaron bandwidth ranged from 0.052 to 0.148 eV in the adiabatic region, and the value was <0.030 eV in the non-adiabatic region. The hopping carrier mobility varied from 2.65×10−6 to 2.90×10−4 cm2 V−1 s−1 at 473 K. The carrier density was obtained to be of the order of 1020–1021 cm−3, and temperature dependence of the carrier density was barely present between 423 and 473 K. The conductivity of the present glasses was primarily determined by hopping carrier mobility.