A Si K-edge XANES study of Ti containing alkali/alkaline-earth silicate glasses

Abstract

Si K-edge X-ray absorption near edge structure (XANES) spectra were collected from Ti-bearing alkali and alkaline-earth silicate glasses with metasilicate (R 2O/SiO 2) compositions where R=Na 2O, K 2O and CaO. The Si K-edges of the Na 2SiO 3, K 2SiO 3, and CaSiO 3 glasses containing TiO 2 are observed at ∼0.8, ∼0.9, and ∼1.0 eV lower energy than that of silica glass (a-SiO 2), respectively, and shift to higher energy with added TiO 2. This indicates that the glasses are less polymerised than a-SiO 2 but become more polymerised with increasing TiO 2. Ti is predominantly acting as a network former and this is reflected at the local Si environment as an increase in polymerisation. A broad resonance near ∼1864 eV is related to the average Si–O–Si angle and/or the Si–O bond strength. In addition, a resonance observed at ∼2–5 eV above the absorption edge is located at a similar energy to one assigned to [6]Si in silicophosphate glasses and may interfere with resonance area calculations used to quantify [6]Si in those glasses. The presence of this resonance indicates changes in the median range structure; in particular, changes in the oxygen environment surrounding the Si atoms.