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

Crystallization behavior of alpha-AgI was investigated by means of XRD, DSC , and FE-SEM from the melts and glasses of AgI-Ag2O-MxOy (MxOy = B2O3, GeO2 , WO3). alpha-AgI microcrystals were formed by rapid quenching of melts wit h around 80 mol% AgI and also by heating of glasses with around 75 mol% AgI . In any system, alpha-AgI fine particles of about 20-40 nm in diameter wer e dispersed in the composites from the melts; there were no marked differen ces in microstructure among the samples in those systems. The alpha-AgI mic rocrystals included in the composites obtained from the melts had a large h eterogeneous lattice strain at room temperature. The samples of those syste ms 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% A gI, for which no X-ray crystalline peaks were observed. In those glasses be ing heated up to 95-120 degrees C, island regions of several hundreds of na nometers were observed; the island regions contained finely dispersed alpha -AgI particles of about 20-30 nm in diameter. It is noteworthy that the cry stallization temperatures of alpha-AgI are much lower than the a-p phase tr ansformation temperature (147 degrees C). The crystallization of a-AgI from the glass below the alpha-beta phase transformation temperature supports t he possibility of the existence of alpha-AgI nuclei in the AgI rich amorpho us particles in the as-quenched glasses with 75 mol% AgI. (C) 1999 Publishe d by Elsevier Science B.V. All rights reserved.