ON THE ELECTRONIC CONDUCTIVITY OF COMPOSITE ELECTROLYTES

The general problem of the distribution of minority charge carriers (electrons) in space-charge regions is discussed. It is shown that their profile is assuming boundary equilibrium, determined by the behavior of the majority charge carriers (ions). This result also has an important implications for semiconductors. The contribution of electrons to the excess conductivity of space-charge regions is calculated for one interface as well as for a dispersion. The Wagner-Hebb technique is extended to the problem of a nonuniform defect concentration in the quasi-parallel switching approximation. Wagner-Hebb experiments are performed on AgCl:γ-Al2O3 composites. An increase in both n- and p-type conductivity is found with respect to pure AgCl. Applying the space-charge model, the result can be explained by a double effect. Impurities are introduced (homogeneous doping) and enhance the hole concentration in the bulk (detected by the high-T behavior); space-charge effects (heterogeneous doping) due to the interaction of the γ-Al2O3 surface with the silver cations (indicated by the influence on the ionic conductivity) enhance the n-conductivity in the space-charge regions. The homogeneous effect is presumably due to O doping and is consistent with literature results on AgI-, LiI- and CuCl-alumina composites.