Mechanism of hopping conduction in new CeO2-B2O3 semiconducting glasses

CeO2-B2O3 glasses having a broad range of compositions, prepared by a press-quenching method from glass melts, were studied for DC conductivity. The conductivity at 583K (1000/T= 1.715K(-1)), In sigma(583), increases by about 16% in the composition regime 20-50mol% CeO2 while in the composition range 50-60mol% CeO2, ln sigma(583) decreases by about 28%. The behavior of In sigma(583) with composition can be interpreted in terms of the changes in the high-temperature activation energy Wand the hopping distance, R. Between 20 and 50mol% CeO2, increasing the mechanical strength and cross-linking of the glass network results in decreasing the polaron hopping energy, W-H. At higher concentrations, the breaking of the 3D network observed to be probable for these glasses may increase the disorder energy, W-D. The conduction mechanism is found to be non-adiabatic in nature for glasses investigated. Mott's model for the small polaron hopping conduction between nearest-neighbors gives unreasonable values for the Ce-Ce distance and the phonon frequency of the lattice vibrations. The increase in the conductivity with temperature can be interpreted in terms of the Schnakenberg model for optical multiphonon assisted hopping process at high temperatures and single optical phonon process at the lower ones. This model gives reasonable values for the phonon frequency of the lattice vibrations, the polaron hopping energy, and slightly higher values of W-D. (c) 2006 Elsevier B.V. All rights reserved.