A. C. conductivity due to intimate pairs of charged defect centres

The influence of the association of charged defects into intimate pairs on a.c. conduction is discussed in the light of the fundamental mechanism being that of the simultaneous hopping of two electrons over the barrier separating two oppositely charged defect centres, the barrier height being correlated with the intersite separation via the Coulomb interaction. The behaviour of chalcogenide glasses is discussed in terms of the present theory, and it is concluded that the existence of two classes of a.c. conductivity behaviour into which these materials generally fall can be simply explained by the predominance of either intimate pairs or non-intimate pairs of charged defect states according to the conditions of preparation.