Patent ID: 7300896

Claim:
A glass ceramic comprising the following components (in wt.-% on oxide basis): SiO 2 35-60 B 2 O 3 >4-10 P 2 O 5 0-10 Al 2 O 3 16.5-40 TiO 2 1-10 Ta 2 O 5 0-8 Y 2 O 3 0-6 ZrO 2 1-5 MgO 6-20 CaO 0-10 SrO 0-4 BaO 0-8 ZnO 0-4 SnO 2 + CeO 2 0-4 SO 4 2− + Cl − 0-4, wherein the total content of SnO 2 , CeO 2 , SO 4 2− and Cl − Σ(SnO 2 , CeO 2 , SO 4 2− , Cl − ) is between 0.01 wt.-% and 4 wt.-%; the glass ceramic having at most 0.5 wt % alkali metal oxides Σ(Li 2 O, Na 2 O, K 2 O, Rb 2 O,Cs 2 O).