Crystallization of sodium digermanate, Na2Ge2O5, from Na2O-GeO2 glasses

Average single bond strength and optical basicity of Na2O-GeO2 glasses

“…The results obtained in the present paper on the single bond strength of sodium germanate glasses by applying the thermodynamical approach proposed by Takahashi and Yoshio are in agreement with O1s and Ge3d XPS results reported by Gee et al 12) On this basis it is possible to suggest that the increase of the optical basicity with decreasing of the single bond strength until 25 mol% Na2O in Fig. 3 is caused by the formation of Ge (4) -O-Ge (6) bridging bonds along with the presence of Ge…”

“…32) High energy component is attributed to BO and low energy component to NBO, due to the higher effective charge of the latter. Therefore the increase in optical basicity with decrease of the single bond strength of Na2O-SiO2 glasses could be explained with the decrease of the number of strong covalent Si (4) -O-Si (4) bridging bonds and the increase of the number Si (4) -O -…Na (6) bonds which possess highly polarizable non-bridging oxygen.…”

“…Ge (4)-O-Ge (4) bonds and second assigned to NBO in Na-O-Ge (4) bonds, respectively. On this basis we assume that N3 in Table 2 in fact represents the fraction of GeO4 groups with one nonbridging oxygen denoted as [GeO4] -NBO.…”

“…12)-14) For example 17 O two-dimensional NMR spectra for Na2O-GeO2 glasses have shown the existence of both bridging oxygen linking Ge (4) and highly coordinated Ge (Ge (5,6) -O-Ge (4) ) and nonbridging oxygen (Note that as superscript in bracket the coordination number of germanium is given). An increase in topological disorders is demonstrated at the density maximum, manifesting the atomic origin of anomaly.…”

“…-O-Ge (4) in the glass structure. Since the germanate anomaly effect is observable at about 20 mol% Na2O, this result supports the idea that the formation of GeO6 groups is a main reason for the effect.…”