Structure of silver iodide/silver selenate fast-ion-conducting glasses: neutron diffraction experiments

Structure factors, S(Q), of many fast-ion-conducting glasses show peaks at very low momentum-transfer values, (h) over bar Q, which can be attributed to a characteristic intermediate-range order. We report on a neutron diffraction study of the fast-ion-conducting glass-forming system x(AgI)(2).(1-x)Ag2SeO4 with x approximate to 0.5 in the glassy, partly crystallized, and liquid states. The structure factors of the glass and the melt art: similar: the very-low-Q peak (VLQP) at Q approximate to 0.75 Angstrom(-1) survives the melting process and shifts towards higher Q-values with increasing temperature. The partly crystallized glasses show Bragg peaks at around 0.8 Angstrom(-1), whereas no intensity in this Q-range has been observed for crystalline silver selenate. In the glasses, the intensity of the VLQP increases with AgI content and its position shifts towards lower Q. The origin of this peak is discussed. The peaks observed in S(Q) art:assigned to various ionic species, and coordination numbers for these species, are derived from the total pair correlation functions, T(r).