Abstract
The germanate anomaly, wherein the glass transition temperature of alkali germanate glasses first increases and then decreases due to increasing coordination of Ge followed by the formation of non-bridging oxygen has been extensively discussed. However, a lesser known, second anomaly in which the glass transition temperature initially decreases to a minimum near 3 mol% alkali oxide has long evaded explanation. Here we report high-resolution Raman spectroscopy findings that clearly demonstrate how the coordination change of Ge is delayed in favor of non-bridging oxygen formation at low alkali contents causing the peculiar dip in glass transition temperature.