Superionic Conduction in SilverIodide and Silver ChromiumSulfide
Abstract
During the past few years there has been a renewed interest in the studies of solid electrolytes for two reasons: (i) they stand a high potential for technical applications and (ii) being somewhat intermediate between solids and liquids, they provide interesting systems for theoretical studies. The present investigation is in line with the latter of the above two reasonings. It deals with the influence of mutual interaction and concentration of the mobile Ag ions in the superionic conductor (alpha)AgI on their distribution and transport. Also an exact calculation for the temperature dependence of the ionic conductivity of a twodimensional superionic conductor AgCrS(,2) is presented. This study started with a calculation of the configurational entropy of silver ion distribution in the superionic conductor (alpha)AgI, using the cluster variation method (CVM). Then, starting with a formulation of ionic conductivity based on Kubo's theory, as applied to a lattice gas model with nearestneighboring hopping, an exact closed form expression for the dynamical currentcurrent correlation functions was obtained. First this formulation was applied to the study of the conductivity of (alpha)AgI, where the required occupation number correlation functions were evaluated using the CVM. Later, the above formulation was used for AgCrS(,2) which provides a prototype for the twodimensional conduction on a halffilled honeycomb lattice. Here an exact calculation becomes possible in analogy to the Ising model. The configurational entropy results for (alpha) AgI compare well with experiment and suggest the existence of strong shortrange correlations among the silver ions. The ionic conductivity of (alpha)AgI is found to increase with the nearestneighbor repulsion between Ag ions until the nearestneighbor sites of an occupied site become vacant. The concentration dependence of the conductivity seems to indicate that the naturally occurring composition (one Ag ion per six tetrahedral sites) of mobile ions happens to have the highest conductivity. For AgCrS(,2) the theoretically calculated temperature dependence of the ionic conductivity agrees fairly well with experiment. The inclusion of correlated hops might improve the agreement on the low temperature side.
 Publication:

Ph.D. Thesis
 Pub Date:
 1982
 Bibcode:
 1982PhDT........99S
 Keywords:

 A THEORETICAL STUDY;
 Physics: Condensed Matter