An x-ray diffraction and P-31 MAS NMR study of rare-earth phosphate glasses, (R2O3)(x)(P2O5)(1-x), x=0.175-0.263, R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er

An x-ray diffraction and P-31 MAS NMR study of rare-earth phosphate glasses of composition, (R2O3)(x)P2O5)(1-x), where x = 0.175-0.263 and R = La-Er ( except for Pm), is presented. The structures of these materials were invest igated as a function of (a) rare-earth atomic number and (b) glass composit ion, The results show an increase in rare-earth coordination number from si x to seven as the rare-earth ion increases in size. This effect is most evi dent for the rare earths, Ce, Pr and Nd, and appears to be independent of c omposition variation. The implications of sevenfold coordination in these g lasses with respect to the possibilities of rare-earth clustering are discu ssed, as is the role of the incorporation of aluminium impurities in this r egard. The increase in levels of cross-linking within the phosphate network , as a consequence of these small amounts of aluminium, is illustrated, as is the changing nature of the phosphate groups as a function of composition . The first reliable and quantitative parametrization of the second and thi rd neighbour R-(O)-P and R-(OP)-O correlations is also given and the stabil ity of the structures to strain when the glasses are drawn as fibres or exp osed to different thermal conditions is described.