Abstract Glasses in the system BaO/TiO 2(ZrO 2)/Al 2O 3/B 2O 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 2B 2O 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.