Anion effect on the structure of Ag₂S–AgPO₃ superionic glasses

Abstract

We report on time-of-flight neutron diffraction data measured on superionic-conducting glasses (Ag₂S)_x(AgPO₃)_{1− x} with x=0.5 and 0.7 at room temperature via the High-Intensity Total Scattering (HIT-II) instrument at KENS and we contrast the results with AgPO₃, (AgI)_0.5(AgPO₃)_0.5 and (AgI)_0.33(Ag₂S)_0.33(AgPO₃)_0.34 glasses. The structure factor of (AgI)_0.5(AgPO₃)_0.5 shows a strong prepeak at low Q∼0.8 Å⁻¹ in contrast to the undoped glass AgPO₃ where there is no prepeak. In the Ag₂S–AgPO₃ system the prepeak appears only very weakly and the difference between radial distribution function (RDF) of doped and undoped glasses show peaks at 2.15, 2.55, 2.75 and 3.0 Å, corresponding to PS, AgS, SS and SO distances, respectively. Both doped systems form superionic-conducting glasses, but the sulfide ion is largely incorporated into the phosphate tetrahedra, breaking down the corner-sharing chains into discrete PSO₃ tetrahedra.