CONDUCTIVITY AND PERMITTIVITY MEASUREMENTS OF FAST ION CONDUCTORS IN THE MICROWAVE REGION.

摘要

This work is on the conduction and dielectric properties of fast ion conductors in the microwave and radio frequency regions. While solids possessing high ionic conductivity have been known for a long time, they have received relatively little attention until the late sixties when their potential application as solid electrolytes was first advocated. As microwave dielectric measurements have the necessary resolution in time scale to reflect the transport mechanism of the mobile ion, much attention has been focused onto this branch of study in solid state ionics. However, due to difficulties in experimental technique, reported spectra on fast ion conductors are rather few. In this work, techniques of microwave dielectric spectroscopy pertinent to fast ion conductors are studied. Special effort is devoted to polycrystalline materials. Ag(,2)HgI(,4) is chosen as the model material for this investigation due to its well-characterized structure, high stability, and its possession of an order-disorder phase transition at (TURN)50(DEGREES)C. Observed spectra and thermal activation effects reveal distinctive features separating the ionic conducting (alpha)-phase (above 50(DEGREES)C) from the electronic conducting (beta)-phase (below 50(DEGREES)C). Transport processes in the former can be described by hopping models whereas those in the latter can be accounted for as the remains of the infrared oscillator mode. Based on rate theory, a simple model giving the dielectric response associated with hopping conduction is constructed. It is demonstrated that in order to give a realistic description of ionic motion in the dc limit, one must consider the flux of ion across the potential barrier rather than the rate of change of polarization or the continuity equation. Explicit equations relating the complex conductivity to lattice parameters and temperature are derived.