Abstract
It has been commonly understood in alkali germanate glasses that tetrahedral GeO4 and octahedral GeO6 units construct the glass networks. It is also believed that a glass has a frozen structure at the melted state. According to this common knowledge, GeO6 units should be present also in the melts. Actually, Kamiya et al. (1986) reported that the melts had the same structure with the corresponding glasses based on the high temperature diffraction studies. In the present study, structural change has been investigated by using a molecular dynamic simulation. In the glass models obtained at room temperature, GeO5 units were formed as well as GeO4 and GeO6 units. When the glass models were heated, GeO5 and GeO6 units having higher coordination numbers turned into GeO4 units. It was therefore suggested that the melts had a different structure with the glasses, and Ge atoms in the melts preferred lower coordination structures.
