EFFECT OF HEAT-TREATMENT ON RAPIDLY QUENCHED AGI-BASED SILVER ORTHOBORATE CLASSES CONTAINING LARGE AMOUNTS OF AGI

The effect of heat treatment on the twin-roller rapidly quenched 75AgI . 18.7Ag(2)O . 6.3B(2)O(3) glass was investigated by differential sca nning calorimetry (DSC), high-temperature X-ray diffraction (XRD), and field-emission-type scanning electron microscopy. The glass had an in homogeneous microstructure with dispersed particles 40-60 nm in diamet er at room temperature. On the other hand, island regions of several h undred nanometers with fine dispersed particles about 20-30 nm in diam eter were observed in the glass after heating to 120 degrees C. DSC an d high-temperature XRD measurements revealed that crystallization occu rred at around 120 degrees C, which is lower than the alpha-beta phase transformation temperature (147 degrees C), to form alpha-AgI in the glass. The crystallization of alpha-AgI from the glass below the alpha -beta phase transformation temperature strongly supports the possibili ty of the existence of alpha-AgI nuclei in AgI-based silver orthoborat e glasses. Validating the existence of AgI microcrystals supports the microdomain model for superionic AgI-based glasses.