Lithium germanosilicate glass formation, kinetics, stability and crystallization

Lithium disilicate glass (Li2O center dot 2SiO2) was modified using GeO2 resulting in compositions Li2O center dot 2GeO2 center dot 2SiO2 (L1G2S2), Li2O center dot GeO2 center dot SiO2 (L1G1S1), and GeO2 center dot SiO2 (L0G1S1). The glass formation was investigated and confirmed for compositions L1G2S2 and L1G1S1 through differential thermal analysis and X-ray diffraction. Two heat treatments were conducted in order to form a glass-ceramic and a sample with a larger crystalline fraction. The crystalline phase was identified through X-ray diffraction as a Li2(Ge,Si)2O5 solid solution of lithium silicate (PDF 010-70-4856). Raman spectra of all samples were analyzed and discussed. The presence of bands associated with Ge in defect sites in silica glass, and those associated with Si-O-Ge bonds suggest the network is established by both SiO2 and GeO2 and not two separate networks, which is consistent with the formation of a solid solution. The refractive index was measured for the glasses and glass-ceramics samples, revealing a very small dispersion between 0.3 and 0.8 mu m.