X-RAY-DIFFRACTION STUDIES OF RARE-EARTH METAPHOSPHATE GLASSES

X-ray diffraction measurements have been performed at the Synchrotron Radiation Source, Daresbury, UK, in a structural study of the rare-ear th metaphosphate glasses (Pr2O3)(0.216)(P2O5)(0.794), (Eu2O3)(0.252)(P 2O5)(0.748) and (Tb2O3)(0.26)(P2O5)(0.74), whose compositions were det ermined by electron microprobe analysis. Such rare-earth metaphosphate glasses R(PO3)(3) containing high concentrations of rare-earth R(3+) ions are of growing interest in fundamental studies of magnetic glasse s and in optical communications and laser technologies. The diffractio n results prove to be consistent with a network model which is dominat ed by a phosphate glass skeleton having three-dimensional connectivity , constructed from PO4 tetrahedra linked to adjacent tetrahedra via br idging oxygen atoms. Results relating to rare-earth-oxygen correlation s are consistent with a sixfold to eightfold coordination of the rare- earth atoms, with distances showing the trends expected from the lanth anide contraction: a reduction of the rare-earth ionic radii with incr easing atomic number.