SPECTROMAGNETIC EVIDENCE FOR SPATIAL CORRELATION OF COPPER CENTERS IN PHOSPHATE-GLASSES AND ITS EFFECT ON THE CHARGE-TRANSPORT PROCESSES

Copper-containing zinc phosphate glasses have been studied for copper contents up to 15 mol% by changing the non-metal-to-metal ratio of the matrix. Optical measurements in the u.v.-visible range as well as e.s.r. analyses were carried out in order to provide structural information about the copper configuration in the system. Strong evidence was obtained for the existence of two different copper pairs. In view of these results and using a modified form of the equation of Austin and Mott for the d.c. conductivity, an analysis of the role of the spatial correlation of copper centers in fixing the hopping behaviour was performed, which stresses the importance of introducing a realistic description of the coordinative geometry of the transition-metal ion in the conductivity model in order to give a full account of the electrical behaviour of the system.