Neutron diffraction and exafs evidence for TiO 5 units in vitreous K 2O · TiO 2 · 2SiO 2

Abstract

A combination of neutron diffraction and X-ray absorption spectroscopic techniques has been used to investigate the Ti coordination in vitreous K 2O· TiO 2 · 2SiO 2. In the former case, the Tizz.sbnd;O bond lengths have been studied using the technique of isotopic substitution. XANES (X-ray absorption near-edge structure) data indicate that there is little or no evidence for a centre of inversion symmetry at the Ti site in the glass. TiO bond distances derived from neutron diffrraction and EXAFS (extended X-ray absorption fine structure) agree to within 0.03 Å and it is concluded that the Ti is present as TiO 5 tetragonal pyramids containing one non-bridging oxygen atom associated witth a titanyl bond ( Ti=0 = 1.65 A ̊ ). The bridging TiO bond length is 1.96 Å and TiTi correlations occur at 3.4 Å and 6.1 Å.