A NEUTRON AND X-RAY-DIFFRACTION STUDY OF THE STRUCTURE OF THE LAP3O9 GLASS

A study of La metaphosphate glass using a combination of neutron and X -ray diffraction has yielded reliable information on the La-O coordina tion and the spatial distribution of the La3+ cations. Due to the real -space resolution of the neutron diffraction experiment, it was possib le to observe two different P-O bond lengths in the PO4 tetrahedron. T he La-O coordination number of about 7 exceeds the number, 6, of termi nal oxygen atoms available for the coordination of each of the La3+ ca tions. This leads to a tendency for clustering of the LaOn polyhedra, which is also observed in complementary reverse Monte Carlo results. T he first feature visible in the X-ray structure factor at a scattering vector magnitude, Q, of 12 nm(-1), is related to a La-La peak in real space at about 640 pm. This corresponds to La-La neighbours which are separated by a PO4 unit. (C) 1998 Elsevier Science B.V. All rights re served.