TRANSPORT-PROPERTIES OF SEMICONDUCTING FE2O3-PBO-B2O3 GLASSES

Density, DC conductivity and B-11 wide-line NMR investigations have been carried out for xFe2O3-(50 - x)PbO-50B2O3 glasses (0 less-than-or-equal-to x less-than-or-equal-to 20 mol%). The NMR spectra indicated the formation of non-bridging oxygen ions in the borate network upon introducing Fe2O3. The DC conductivity and the activation energy for conduction change markedly with Fe2O3 content. The high-temperature conductivities can be described by Mott's model for the phonon-assisted hopping of small polarons. The polaron hopping is shown to be non-adiabatic. The low-temperature conductivities are characterized by the variable-range hopping mechanism. For Fe2O3 contents greater than 15 mol%, glass-crystal composites are formed, changing greatly the electrical properties, and other conduction mechanism is to be assumed.