The coordination environment of Ti in eight Ti-bearing glasses of the Na2Si4O9-Na2Ti4O9 join (NTS) and in six ATY2 glasses (A2O·TiO2·2YO2, with A = Na, K, or Rb and Y = Si or Ge) was determined using high-resolution, X-ray absorption near-edge structure (XANES) spectroscopy at the Ti K edge in ambient conditions.
Fivefold-coordinated Ti (Ti) is the dominant Ti species (≥50 ± 10% of the total Ti) in all the glasses studied. Sixfold-coordinated Ti was detected mostly in sodic glasses (NTS, NTS2, NTG2), and it increases with TiO2 content (as high as 40 ± 10% of the total of Ti in the most TiO2-rich NTS glasses) and in the order Si < Ge. Fourfold-coordinated Ti was detected only in nonsodic ATY2 glasses, and its content increases in the order Na < K < Rb and Ge < Si. Fivefold-coordinated Ti4+ is probably present as square pyramidal, titanyl-bearing moieties, or (Ti=O)O4.
A synthesis of Ti4+ coordination for oxide glasses derived using direct methods (X-ray absorption and neutron scattering) can be used, for instance, to help in the interpretation of Raman scattering spectra collected for Ti-bearing glasses and to estimate NBO/T ratios better for titanosilicate glasses and melts.