Small polaron hopping conduction in V 2O 5–Sb–TeO 2 glasses

Abstract

The dc electrical conductivity of glasses in the system V 2O 5–Sb–TeO 2 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⩽TeO 2⩽100 mol%, 0⩽V 2O 5⩽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 V 2O 5 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 V 2O 5 and Sb. A glass of composition 70 V 2 O 5 · 20 Sb · 10 TeO 2 (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 1 2 Θ D ( Θ D : the Debye temperature); the electrical conduction at T> 1 2 Θ D was due to adiabatic small polaron hopping of electrons between vanadium ions for V 2O 5⩾50 mol%, and non-adiabatic for 30⩽V 2O 5<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 cm 2 V −1 s −1 at 473 K. The carrier density was obtained to be of the order of 10 20–10 21 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.