X-ray absorption study of Ti-bearing silicate glasses

Abstract

Abstract. Ti K-edge XANES spectra have been collected on a series of Ti-bearing silicate glasses with metasilicate and tetrasilicate compositions. The intensity of the preedge feature in these spectra has been found to change with glass composition and varies from 29 to 58% (normalized intensity) suggesting a variation in structural environent around the absorbing atom. The pre-edge peak intensity increases for the alkali titanium tetrasilicate glasses from 35% to 58% in the order Li<Na<K<Rb, Cs whereas for the metasilicate compositions there is a maximum for the K-bearing glass. The pre-edge peak intensity remains constant for the alkaline earth titanium metasilicate glasses, Ca and Sr (34%) but increases slightly for Ba (41%). As the intensity of this feature is inversely correlated with coordination number, a comparison of the pre-edge intensity data for the investigated glasses with those of materials of known coordination number leads us to establish a regression equation and to infer that the average coordination number of Ti in these glasses ranges from 4.8 to 5.8. Large alkali cations appear to stabilize a relatively low average coordination number for Ti in silicate melts. The Ti structural environment results appear also to vary as a function of SiO 2 content within the K20-TiO2-SiO2 system.A number of physical properties of the melts from which these glasses were quenched and of other Ti-bearing silicate melts, have been determined in recent years. Clear evidence of a variable coordination number of Ti, consistent with the interpretation of the present XANES data is available from density measurements. These and other property determinations are compared with the present spectroscopic observations in an attempt to relate structure and properties in these melts which contain a major component with variable coordination number.

Environment of titanium and aluminum in a magnesium alumino-silicate glass

“…27 Al 1D NMR experimental spectra and the fitting models obtained with parameters given in table 2 (top) and contour plots of 27 Al MQ-MAS NMR spectra (bottom) for the (a) 2MgO-2Al 2 O 3 -5SiO 2 (COR) glass and for the (b) 2MgO-2Al 2 O 3 -5SiO 2 -TiO 2 (Ti-COR) glass. and [6] Al exist in this glass, as is observed in other Ca-aluminosilicate glasses [35] and Mg-alumino-silicate glasses [36,37]. When introducing titanium in the melts, we observe a slight increase of the chemical shift (δ iso ) and of the quadrupolar coupling constant (C Q ) of each site that can be correlated to an increased distortion of the Al environment.…”

“…In the RMC model the coordination distribution can be resolved, giving 21% of total titanium atoms in fourfold coordination, 51% in fivefold coordination and 28% in sixfold coordination. All methods used to determine the coordination number distribution for Ti atoms agree on the predominance of [5] Ti, with the coexistence of [4] Ti and [6] Ti in similar amounts. This is an important difference with other alkaline or alkaline-earth silicate glasses (see [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]) that usually present a strong preference for [5] Ti with minor amounts of [4] Ti.…”

“…The environment of titanium has been mainly investigated in the TiO 2 -SiO 2 binary system [3][4][5] and Ti-bearing alkali or alkaline-earth silicate glasses [6][7][8][9][10][11][12]. All these studies show that titanium atoms are present in the glass with multiple coordination numbers from four to six.…”

“…Alkaline-earth alumino-silicate glasses with 5 mol% TiO 2 contain both [4] Ti and [5] Ti ( [5] Ti ∼ 60-75 ± 10% of the total Ti), while in alkali alumino-silicate glasses the presence of Al in the glass causes some [5] Ti to transform into [4] Ti, with a maximum of about 40% of [4] Ti. There is little evidence from XAS for a significant amount of [6] Ti (estimated <20%). The first studies on Mg-alumino-silicate glasses have been reinterpreted with the presence of major amounts of [5] Ti [9,[17][18][19].…”

“…Computer modeling of the diffraction data was performed using the reverse Monte Carlo method to provide a structural model of the 2MgO-2Al 2 O 3 -5SiO 2 -TiO 2 glass. The detailed Ti coordination is obtained showing the existence of a mixture of [4] Ti, [5] Ti and [6] Ti. The presence of TiO 2 modifies the alumino-silicate network, favoring the formation of fivefoldcoordinated aluminum atoms, [5] Al.…”