Structure of a potassium germanophosphate glass by x-ray and neutron diffraction

An increase of the Ge-O coordination numbers in binary germanate glasses with change of the K2O or P2O5 content, respectively, was previously found by diffraction experiments. The present work is aimed at clarifying the concomitant effect of both oxides. X-ray and neutron diffraction of high resolving power was used to characterize the ternary glass of nominal composition (K2O)0.125-(P2O5)0.375-(GeO2)0.50. Gaussian fitting of the P-O and Ge-O nearest-neighbour peaks in the correlation functions results in coordination numbers of 3.8±0.2 and 5.1±0.2, respectively, with distances of 0.153±0.001 or 0.183±0.002 nm, respectively. These parameters are consistent with a network formed of PO4 and GeOn polyhedra with n=4,5, or 6 where Ge-O-P bridges dominate. The K+ ions coordinate terminal oxygens of the PO4 units. The first diffraction peak appears at a small value of ∼7 nm−1 that deviates considerably from that of other oxide glasses.