Multiphonon tunneling conduction in vanadium-cobalt-tellurite glasses

Ternary vanadium oxide glasses in the system V2O5-CoO-TeO2 are fabricated b y press quenching of glass melts, and de conductivities (sigma) are investi gated at temperatures from 330 to 475 K for different glass compositions. F rom the study of the phase diagram, the glass formation region is found to be in the range of V2O5=0-85 mol%, CoO = 0-35 mol%, and TeO2 = 25-100 mol % . These glasses contain microcrystalline clusters dispersed in the glass ma trix. In the high-temperature regime above Theta(D)/2 (Theta(D) is the Deby e temperature), the small polaron hopping model is found to be applicable. In the low temperature (below Theta(D)/2) regime, however, both Mott's vari able-range hopping and the Greaves' intermediate range hopping models are f ound to be not applicable. The most probable transport for the entire range of temperature and compositions is concluded to be due to multiphonon tunn eling of large polarons between the microclusters, supporting the model pro posed by Shimakawa. [S0163-1829(99)03029-5].