CORRELATION EFFECTS ON FREQUENCY-DEPENDENT CONDUCTIVITY - APPLICATION TO SUPERIONIC CONDUCTORS

The Scher-Lax model for the calculation of a.c. conductivity is modified to allow for temporal and spatial correlations. If, due to, say, lattice relaxation effects, a charge is most likely to continue to move in the same direction (caterpillar mechanism), then the real part of the conductivity will saturate, at large frequencies, below the d.c. level. The reverse will be true if a bounce-back mechanism dominates. These two cases of correlation can be related to the behavior of the superionic conductors AgI and Na β-alumina, respectively. The degree of disorder in the hopping sites determines the distribution of ionic transition rates which in turn governs the details of the conductivity curve. The frequency dependent conductivity due to the motion of an ionic cluster (dimer) is also analyzed. © 1979.