The change of the Ge–O coordination number in potassium germanate glasses probed by neutron diffraction with high real-space resolution

The Germanate Anomaly: What do we know?

“…More recent high resolution neutron diffraction studies of the germanate anomaly provide better evidence for the presence of a higher coordinated Ge species in alkali-germanate glasses. Both the neutron scattering studies of Ueno et al [9] and Hoppe et al [13] observe a shoulder on the high r side of the first peak in their radial distribution functions which they associated with a higher coordinated Ge site. In both studies, the maximum in the Ge-O length calculated from their data is at 20 mol% alkali-oxide.…”

“…Furthermore, subsequent X-ray and neutron scattering [8][9][10][11][12][13] and EXAFS [14][15][16][17][18][19] studies observed a lengthening of the average Ge-O bond length with addition of alkalis ( Fig. 4(a)).…”

“…Despite this apparent paradox, the high-resolution neutron scattering data noted above [9,13] clearly show that a higher coordinated Ge species occurs in alkali-germanate The estimated error for the CN is 20%. An error bar is shown for a CN of 4 ± 10%.…”

“…glasses. In addition, it has been suggested that this species may be 5-fold Ge ( [V] Ge) [9,13,22]. However it must be noted that the occurrence of this species does not correlate with the germanate anomaly.…”

“…Fig. 6(a) shows a plot of the curve fits by Hoppe et al [13] to their 11 and 20 mol% K 2 O-GeO 2 neutron data. The fits show that there are [13] along with the densities for 10 and 20 mol% K 2 O-GeO 2 glasses.…”