Chapter 11: R₂O–M₂O₃–GeO₂ Glasses Check Access

Alkali alumino- and gallogermanate glasses can be formed over large composition regions. Replacement of alkali oxides by alumina or gallium oxide decreases the density, refractive index, and thermal expansion coefficient while increasing the electrical conductivity and the glass transformation temperature and transformation range viscosity of these glasses. The germanate anomalies in the densities of the sodium and rubidium aluminogermanate glasses and the high alkali anomaly in the glass transformation temperature of the sodium and potassium aluminogermanate glasses disappear when R₂O to Al₂O₃ is equal to or greater than one. This effect only occurs for the alkali gallogermanate glasses when the R₂O to Ga₂O₃ ratio exceeds unity. The density and refractive index of thallium aluminogermanate glasses increase in density and refractive index as the Tl₂O content increases but decrease as Al₂O₃ replaces Tl₂O. Indium oxide increases the density and refractive index of R₂O–In₂O₃–GeO₂ glasses (R is Li, Na, or K) relative to GeO₂, Al₂O₃, and Ga₂O₃. The glassforming regions in these systems are much smaller than those of the corresponding alumino- and gallogermanate systems.