The environment of Dy3+ cations in a sodium borosilicate glass

The neutron diffraction technique is employed to investigate the environment of Dy3+ cations in a sodium borosilicate glass matrix of composition 0.210N(a2)O.0.185(11)B(2)O(3).0.605SiO(2), using a special form of the isotopic substitution method, the null technique, in which the neutron scattering length for Dy is set to zero by selecting the appropriate combination of isotopes. This enables the changes in the structure of the base glass, caused by the addition of 13 mol% Dy2O3, to be studied in greater detail. The neutron diffraction data were obtained using the D4c diffractometer at the Institut Laue-Langevin (ILL; Grenoble, France) and were recorded for three samples; the base glass, the base glass incorporating natural Dy2O3 and a similar glass containing Dy-0, where Dy-0 denotes Dy with a zero scattering length. The data are Fourier transformed to yield the real-space total correlation function, T(r), and the first co-ordination shells of the Dy3+ cations are investigated via a peak fit to the isotopic difference correlation function Delta T-Dy(r). The Dy3+ cations are concluded to have an average Dy(O) co-ordination number of 7.3 +/- 0.2, with a first co-ordination shell comprising a distorted octahedron with an average Dy-O distance of similar to 2,31 angstrom, plus one or two further neighbours at higher distances. They appear to be present in DyBO3 chemical groupings, and to be associated with BO33- orthoborate anions.