It was recalled that the alternating-current conductivity which resulted from ion motion in glasses exhibited a power-law frequency dependence which was characterized by an exponent that was less than unity. It had recently been suggested that this exponent depended upon the dimensionality of the local cation conduction space; such that the above exponent decreased with decreasing dimensionality. Measurements were made here of the alternating-current conductivity of 2 metaphosphate glass systems. One was that of superionic glasses which were formed by adding AgI to AgPO3. The other was that of the alkali-metal metaphosphate glasses. In both glass systems, the conductivity exponent varied with the expansion of the phosphate chains which made up the glass network. In the case of the AgI-doped glasses, the exponent increased with increasing expansion of the network. In the alkali-metal series, it decreased with expansion. However, when the exponent was considered to be a function of the so-called constriction (cation size relative to chain separation), the exponent behaved similarly for both glass systems and decreased with increasing constriction of the cation. This decrease was suggested to result from a reduction in the coordination of the cation's local conduction space, which was caused by increasing constriction.

Influence of Cation Constriction on the AC Conductivity Dispersion in Metaphosphate Glasses. D.L.Sidebottom: Physical Review B, 2000, 61[21], 14507-16