ELECTRONIC CONDUCTIVITY IN COPPER-BASED AND IRON-BASED PHOSPHATE-GLASSES EXHIBITING CLUSTERING AND SPINODAL DECOMPOSITION

The results of an extended study of structural, chemical, spectroscopic and electrical properties of oxide glasses are reported. The aim of this investigation was to explore the effect of progressive clustering and incipient spinodal segregation on the electrical properties of glassy oxides. Zinc phosphate glasses containing variable amounts of copper or iron oxides were prepared by quenching and were characterized chemically, electrically and structurally. The transition-metal-ion symmetry in the glass was confirmed to be lower than spherical, with the hopping-centre electronic levels splitting accordingly. In Cu glasses clustering is found to occur and to affect the hopping regime. Furthermore, the matrix structure is seen to affect the glass properties. In iron-based materials, microscopic segregation is additionally observed. Electrical data fulfil the standard hopping-model predictions at very low concentrations only. For total iron contents >5 mol%, spinodal decomposition of super-saturated glassy solutions must be invoked.