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 stu dies of the short- and medium-range order of some phosphate glasses. Detail s 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 combi ne X-ray and neutron scattering data for extracting features of the medium- range order. Increasing Me-0 distances changes the mutual order of the Me a toms in metaphosphate glasses with the tendency of a clustering of Me sites due to MeOn polyhedra sharing oxygen atoms. But if compared with the alter nating order of Me and P sites the clustering of the Me sites is a minor ef fect. Me-Me firstneighbor distances are little affected if the fraction of modifier oxide is varied while the number of Me-Me neighbors is clearly cha nged. (C) 2001 Elsevier Science B.V. All rights reserved.