Anomalous temperature dependence of the first diffraction peak in the superionic glass (AgI)x(AgPO3)1-x

We report neutron-scattering measurements on the first sharp diffraction peak in the superionic conducting glass (AgI)x(AgPO3)1-x as a function of composition x from 0.0 to 0.7. The temperature variation is studied in detail between 300 K and 500 K, a range that spans the calorimetric glass transition. This peak reflects structure in the phosphate network with periodicity d≈10 Å and correlation length ≈25 Å. The intensity of the first sharp diffraction peak shows an anomaly as a function of temperature at a temperature about 6–11 % higher than Tg as measured calorimetrically. This is tentatively ascribed to the diffraction intensity reflecting the onset of α relaxation, while the calorimetric data reflects the onset of β relaxation.