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 pe ak 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 det ail between 300 K and 500 K, a range that spans the calorimetric glass tran sition, This peak reflects structure in the phosphate network with periodic ity d approximate to 10 Angstrom and correlation length approximate to 25 A ngstrom. The intensity of the first sharp diffraction peak shows an anomaly as a function of temperature at a temperature about 6-11 % higher than T-g as measured calorimetrically. This is tentatively ascribed to the diffract ion intensity reflecting the onset of alpha relaxation, while the calorimet ric data reflects the onset of beta relaxation.