Combined neutron and X-ray scattering study of phosphate glasses

The advantage of high resolving power and of different contrast of total X-ray and neutron diffraction (XRD and ND) experiments is demonstrated in studies of the short- and medium-range order of some phosphate glasses. Details of two different P-O bonds are detected using Q-ranges up to 500 nm^-1. A different contrast is used to resolve Me-O distances in the range of the O-O peaks at 0.25 nm where Me is the modifier atom. In many cases the Me-O peaks are asymmetric. Reverse Monte Carlo simulation is applied to combine X-ray and neutron scattering data for extracting features of the medium-range order. Increasing Me-O distances changes the mutual order of the Me atoms in metaphosphate glasses with the tendency of a clustering of Me sites due to MeO_n polyhedra sharing oxygen atoms. But if compared with the alternating order of Me and P sites the clustering of the Me sites is a minor effect. Me-Me first-neighbor distances are little affected if the fraction of modifier oxide is varied while the number of Me-Me neighbors is clearly changed.