Titania is widely considered as an alternative constituent for replacing heavy metal oxides in optical glasses. Its effect on optical properties, however, is complex. This is due to the dielectric properties of the prevalent ionic species, Ti 4+ , the potential co-existence of trivalent titanium, Ti 3+ , giving rise to intrinsic and extrinsic charge transfer reactions, and the existence of different coordination polyhedra, depending on matrix composition. Here, we present a systematic study of the optical properties of the soda-lime-silicate glass system as a function of TiO 2 addition. We consider the silica-rich region of the SiO 2 -Na 2 O-CaO-TiO 2 quaternary, which may be taken as model for a variety of technical glasses. Trends are described in the refractive index, the Abbe number, the optical bandgap and the Urbach energy. The addition of TiO 2 increases the refractive index and the optical dispersion while it lowers the optical bandgap and the Urbach Energy. Results are discussed in relation to relevant literature data towards using titania silicate glasses as high-index replacements for heavy metalcontaining oxide glasses. (Springer-Verlag, 1992 719-724 (1989). 9. R. C. Turnbull and W. G. Lawrence, "The Role of Titania in Silica Glasses," J. Am. Ceram. Soc. 35(2), 48-53 (1952). 10. C. A. Hogarth and M. N. Khan, "A study of optical absorption in some sodium titanium silicate glasses," J. NonCryst. Solids 24(2), 277-281 (1977). 11. M. Villegas, A. de Pablos, and J. F. Navarro, "Caracterización de vidrios del sistema Na 2 O-TiO 2 -SiO 2 ," Bol. Soc. References F. Gan, Optical and Spectroscopic Properties of GlassEsp. Ceram. Vidr. 33(1), 23-28 (1994). 1921-1958 (2005). 44. F. Farges, G. E. Brown, Jr., A. Navrotsky, H. Gan, and J. J. Rehr, "Coordination chemistry of Ti(IV) in silicate glasses and melts: II. Glasses at ambient temperature and pressure," Geochim. Cosmochim. Acta 60(16), 3039-3053 (1996). 45. F. Farges, G. E. Brown, Jr., and J. J. Rehr, "Coordination chemistry of Ti (IV) in silicate glasses and melts: I.XAFS study of titanium coordination in oxide model compounds," Geochim. Cosmochim. Acta 60(16), 3023-3038 (1996). #257129Received 13 XANES studies of synthetic and natural volcanic glasses and tektites at ambient temperature and pressure," Geochim. Cosmochim. Acta 61(9), 1863-1870 (1997). 47. F. Farges, "A Ti K-edge EXAFS study of the medium range environment around Ti in oxide glasses," J. NonCryst. Solids 244(1), 25-33 (1999 373-410 (1976). 50. J. A. Duffy, "Electronic polarisability and related properties of the oxide ion," Phys. Chem. Glasses 30(1), 1-4 (1989). 51. V. Dimitrov and T. Komatsu, "Classification of oxide glasses: A polarizability approach," J. Solid State Chem.178(3), 831-846 (2005). 52. C. W. Ponader, H. Boek, and J. E. Dickinson, Jr., "X-ray absorption study of the coordination of titanium in sodium-titanium-silicate glasses," J. Non-Cryst. Solids 201(1-2), 81-94 (1996). 53. E. Fargin, A. Berthereau, T. Cardinal, G. Le Flem, L. Ducasse, L. Canioni, P. Segon...

In this article, we investigate the correlation of selected physical properties with structural changes in quaternary mixed modifier alkali/alkaline earth oxide silicate glass systems, focusing either on the mixed alkali effect [(20−x)Na 2 O-xK 2 O-10CaO-70SiO 2 (x = 0, 5, 10, 15, 20)] or on the mixed alkaline earth effect [20Na 2 O-(10−y)CaO-yBaO-70SiO 2 (y = 0, 5, 10)]. A maximum microhardness and packing density, as well as a minimum glass transition temperature were observed for mixed alkali glasses. The mixed alkaline earth glasses do not exhibit any clear extrema in any of the properties studied. The hardness and glass transition temperature decreases, while the density and molar volume increases with increasing BaO content.Raman spectroscopy showed an increase in the Q 3 group compared to the Q 2 and Q 4 groups as the high field strength ions Na + or Ca 2+ are substituted by their low field strength analogs K + or Ba 2+ . In the mixed alkali series, the high field strength ion Na + , seems to push the low field strength ion K + into lower energy sites when present simultaneously, while such an effect is not apparent for the mixed alkaline earth glasses, where the far IR spectra of mixed glasses are equivalent to the weighted averages of the pure glasses. K E Y W O R D Smixed modifier effect, silicate glass, glass transition temperature, hardness, Raman spectroscopy and IR spectroscopy 350 | GRUND BÄCK et al.

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