Environment of Ni, Co and Zn in low alkali borate glasses: information from EXAFS and XANES spectra.

XANES spectroscopy confirms that transition elements such as nickel, cobalt and zinc are octahedrally co-ordinated in low-alkali borate glasses, a co-ordination state which is unusual in most oxide glasses. EXAFS spectroscopy indicates that, despite their diluted character, transition elements are inhomogeneously distributed, with a medium range order extending up to 6 Å with multiple scattering features characteristic of the presence of collinear cations. This peculiar structure is attributed to the presence of rigid units in these low-alkali borate glasses. The presence of these ordered domains in 0.1Li2O–0.9B2O3 glasses with NiO contents ranging from 0.5 to 2 wt% shows their independence relative to the concentration of the transition element