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 0·210Na₂O.0·185¹¹B₂O₃.0·605SiO₂, 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 ⁰Dy, where ⁰Dy 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 ΔT_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 ∼2·31 Å, plus one or two further neighbours at higher distances. They appear to be present in DyBO₃ chemical groupings, and to be associated with BO^3– ₃ orthoborate anions.