Sol–gel preparation and properties of TiO2–P2O5 bulk glasses

Monolithic transparent and colorless, or Ti3+-free TiO2–P2O5 glasses containing very large amounts of TiO2 (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol–gel reaction. The density and refractive index n632.8 nm of the sol–gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO2 content of larger than 80 mol% seemed somewhat porous, but n632.8 nm of these glasses was very high as 2.2–2.3. Higher density and higher n632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti4+ ions.