US Patent 9382150 Boron-doped titania-silica glass having very low CTE slope

A boron-doped titania-silica glass containing 0.1 wt % to 8.0 wt % boron, 9.0 wt % to 16.0 wt % TiO2, and 76.0 wt % to 90.9 wt % SiO2. The glass may further include F, Nb, Ta, Al, Li, Na, K, Ca, and Mg, individually or in combinations of two or more, at levels up to 4 wt %. The glass may have an OH concentration of more than 10 ppm. The glass features a CTE slope at 20° C. of less than 1 ppb/K2. The fictive temperature of the glass is less than 825° C. and the peak CTE of the glass is less than 30 ppb/K. The glass has two crossover temperatures and a wide temperature interval over which CTE is close to zero. The uniformity of each crossover temperature relative to its average over a volume of at least 50 cm3 is within ±5° C.