Glass-ceramics in the system BaO/TiO2(ZrO2)/Al2O3/B2O3 and their thermal expansion

Abstract Glasses in the system BaO/TiO 2 (ZrO 2 )/Al 2 O 3 /B 2 O 3 were melted from the raw materials with and without the addition of platinum. They were crystallized in two steps at 720 and 780 °C. TiO 2 does not act as nucleating agent in this system, but widely prevents crystallization. Samples additionally doped with platinum show the crystallization of BaAl 2 B 2 O 7 . However, samples containing equimolar quantities of TiO 2 and ZrO 2 showed the crystallization of this phase without the addition of platinum. The thermal expansion coefficients of samples with TiO 2 -concentration ⩽7 mol% or TiO 2 /ZrO 2 -concentrations ⩽5 mol% exhibit zero or even slightly negative thermal expansion coefficients.