Phase separation in GeO–GeO2 glasses

Abstract

A series of transparent homogeneous amorphous solids between GeO₂ and GeO has been prepared by rapid quenching of liquids and by vapour deposition. Density and refractive index increase smoothly with increasing Ge/O ratio and provide a useful index of composition. Glasses in the range GeO–GeO_1.85 undergo a rapid exothermic transformation when heated above 400°C accompanied by a pronounced blackening, an increase in refractive index, and slight decrease in density. Electron microscopy and diffraction results indicate that the transformation involves the precipitation on a 50–100 Å scale of an amorphous tetrahedrally coordinated Ge-rich phase. The interconnected microstructure so produced is suggestive of spinodal decomposition. A transitional region near GeO_1.9 is characterized by sluggish phase separation kinetics and a dispersed particle morphology suggestive of a nucleation and growth precipitation mechanism. Glasses in the range GeO_1.9–GeO₂ show no evidence for phase separation.