Structure of the glassy fast-ion conductor by neutron diffraction

The structure of the glassy fast-ion conductor (Formula presented) is studied by using the method of isotopic substitution in neutron diffraction. The diffraction pattern measured in a single experiment is separated into its contributions from the partial structure factor (Formula presented) and related difference functions (Formula presented) and (Formula presented) comprising the (Formula presented) and (Formula presented) correlations, respectively, where (Formula presented) denotes a matrix atom (P or S) and (Formula presented) the scattering vector. It is found that the glass structure is significantly different from that of the corresponding crystalline compound (Formula presented) The (Formula presented) units of the crystal are broken up to form tetrahedral (Formula presented) motifs with a P-S bond distance of 2.04(2) Å which are linked to form a matrix having pronounced intermediate-range order. The data for (Formula presented) are consistent with a model wherein the silver ions, coordinated to an average of 2.5(2) S at a bond distance of 2.53(2) Å, move via pathways which have a large distribution of Ag-Ag sites: in real space the Ag-Ag correlations are characterized by a broad “liquidlike” distribution with a nearest-neighbor distance of 2.9(1) Å and coordination number of 1.1(2).