Patent ID: 7091141

Claim:
A glass-ceramic material capable of forming glass-ceramic articles having a surface roughness Ra<75 nm without polishing, containing β-quartz solid solution as the predominant crystalline phase, having a linear coefficient of thermal expansion in the temperature range between 25° C. and 300° C. of ≦10×10 −7 K −1 , a light transmission at 1050 nm of >80% at a thickness of 3 mm, and a composition, by weight of the total composition, comprising 56–67% SiO 2 ; 19–22% Al 2 O 3 ; 3.4–3.8% Li 2 O; 1.8–2.6% ZnO; 1.5–2.5% MgO; 3.3–5% TiO 2 ; 0–2.5% ZrO 2 ; 1.5–3% B 2 O 3 ; 0–6% P 2 O 5 ; 0–0.6% F; less than 500 ppm Fe 2 O 3 ; and components resulting from at least one refining agent.