THE STRUCTURE OF POTASSIUM GERMANATE GLASSES BY EXAFS

Extended X-ray absorption fine structure has been obtained to determin e 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 wi th x = 0.02 - 0.247. The spectra were measured at around liquid helium temperature to eliminate the thermal contribution to the observed str uctural disorder. For all x less than or equal to 0.2, non-bridging ox ygens (NBOs) are produced, as well as GeO6 with the addition of K2O. F or x > 0.2, NBOs continue to increase at the expense of GeO6 units. Mu ch larger structural disorder is found around K in the present glass s eries than around Na in silicate glasses, which suggests that the modi fied random network structure model is less appropriate for these germ anate glasses.