Patent ID: 8143179

Claim:
An essentially colorless, transparent glass-ceramic material containing a solid solution of β-quartz as a principal crystalline phase, having a composition, expressed in percentages by weight on a basis of oxides, consisting essentially of: SiO 2 66-72 Al 2 O 3 18.3-24 Li 2 O 22-5 ZrO 2 2-5 SnO 2 >0.4-3 CeO 2 0-<1 WO 3 + MoO 3 0-<1 CeO 2 + WO 3 + MoO 3 0-<1 Nb 2 O 5 0-3 CeO 2 + WO 3 + MoO 3 + Nb 2 O 5 0-3 MgO 0-3 ZnO 0-4 SrO 0-2.5 BaO 0-2.5 K 2 O + Na 2 O 0-<1 Gd 2 O 3 + La 2 O 3 + Ta 2 O 5 + Y 2 O 5 0-4 Nd 2 O 3 + Er 2 O 3 0-0.1 and Fe 2 O 3 <0.04; wherein, with the exception of inevitable traces, the composition is essentially free of titanium dioxide, arsenic oxide, antimony oxide and phosphates, and the weight percentages of MgO, ZnO, SrO and BaO in the composition are such that (i) MgO+ZnO is in a range of 2.2-4.6, and/or (ii) ZnO+BaO+SrO is in a range of 1-4.