Crystallization of α-AgI from AgI–Ag2O–MxOy (MxOy=B2O3, GeO2, WO3) melts and glasses

Abstract

Crystallization behavior of α-AgI was investigated by means of XRD, DSC, and FE–SEM from the melts and glasses of AgI–Ag 2 O–M x O y (M x O y =B 2 O 3 , GeO 2 , WO 3 ). α-AgI microcrystals were formed by rapid quenching of melts with around 80 mol% AgI and also by heating of glasses with around 75 mol% AgI. In any system, α-AgI fine particles of about 20–40 nm in diameter were dispersed in the composites from the melts; there were no marked differences in microstructure among the samples in those systems. The α-AgI microcrystals included in the composites obtained from the melts had a large heterogeneous lattice strain at room temperature. The samples of those systems showed almost the same degree of lattice strain at room temperature. On the other hand, AgI-rich amorphous particles with 40–60 nm in diameter were dispersed in the twin-roller quenched glasses of any system with 75 mol% AgI, for which no X-ray crystalline peaks were observed. In those glasses being heated up to 95–120°C, island regions of several hundreds of nanometers were observed; the island regions contained finely dispersed α-AgI particles of about 20–30 nm in diameter. It is noteworthy that the crystallization temperatures of α-AgI are much lower than the α–β phase transformation temperature (147°C). The crystallization of α-AgI from the glass below the α–β phase transformation temperature supports the possibility of the existence of α-AgI nuclei in the AgI rich amorphous particles in the as-quenched glasses with 75 mol% AgI.