Isotopic-substitution neutron-diffraction studies of (AgI)(0.5)(AgPO3)(0.5) glass

The superionic glass system (AgI)(0.5)(AgPO3)(0.5) has been studied using isotopic-substitution neutron diffraction with Ag-nat and Ag-107 samples. A number of peaks in the total correlation function T(r) of this four-component glass have been clearly identified by means of a first-difference analysis. Two Ag+ ionic sites were found, with O- or I- environments, but no evidence of AgI clustering was observed. The first- and second-peak intensities in the distinct scattering function i(Q) have been observed to depend on the scattering length of the silver isotope substituted: The Ag-107-substituted sample exhibits a less intense first peak and a more intense second peak than those for the Ag-nat sample. It has been concluded that the doping salt occupies the voids generated by the host-glass density fluctuations in such a way that its correlations tend to cancel the correlations of the host network in the low-e range. This structural picture agrees well with the void model for the origin of the first sharp diffraction peak.