The structure of potassium germanate glasses by EXAFS

Extended X-ray absorption fine structure has been obtained to determine the interatomic distance, R, coordination number (CN) and degree of disorder, Delta sigma(2), around the mobile alkali (K), as well as the network forming (Gel cations of binary xK(2)O .(1 - x)GeO2 glasses with x = 0.02 - 0.247. The spectra were measured at around liquid helium temperature to eliminate the thermal contribution to the observed structural disorder. For all x less than or equal to 0.2, non-bridging oxygens (NBOs) are produced, as well as GeO6 with the addition of K2O. For x > 0.2, NBOs continue to increase at the expense of GeO6 units. Much larger structural disorder is found around K in the present glass series than around Na in silicate glasses, which suggests that the modified random network structure model is less appropriate for these germanate glasses.