VIBRATIONAL SPECTROSCOPIC STUDY OF TI-SUBSTITUTED SIO2

The structure of SiO2-TiO2 glass has been studied at concentrations of titanium from 2.2 to 5.8 mol% by vibrational spectroscopy methods including low-frequency Raman spectroscopy. The glass samples were prepared by vapour deposition of silica and titanium tetrachlorides with concentration of TiCl4 in gas up to 8 vol.%. The temperature of deposition in the flame of hydrogen-oxygen torch was 1640-degrees-C. The Raman spectra were measured in a 90-degrees-geometry using 488 nm light for excitation. The presence of Ti in vitreous silica is indicated in IR and Raman spectra by the appearance of a 935 cm-1 band whose intensity was found to increase monotonicly with increase of Ti content. When Ti is introduced, (i) the bond angle within bridging groups diminishes, (ii) the radius of structure correlation increases; and (iii) the concentration of intrinsic defects in the SiO2 matrix becomes two or three times smaller at Ti content of approximately 4 mol%. With further increase of dopant concentration, it remains the same. Indication of clustering was not observed. Ti-substitution leads to an ordering of the structure of vitreous silica.