The density behaviour of germanate glasses has often been attributed to a change of four-fold Ge to six fold Ge, with subsequent formation of nonbridging oxygens (NBOs). An alternative model involving the formation of three-membered rings, with subsequent NBO formation has been proposed. This paper presents OK-edge XANES results for alkali germanate and sodium germanophosphate glasses with varying Ge:P ratios. The OK-edge can be used to determine the coordination of Ge. No six-fold Ge is observed in any of the glasses except at very high alkali oxide concentrations. The Li2O-, Na2O- and K2O-bearing germanate glasses indicate the presence of five-fold Ge at, but not before, the anomaly maximum, whereas the Rb2O- and Cs2O-bearing germanate glasses exhibit five-fold Ge before the anomaly maximum.
