Patent ID: 7687419

Claim:
A glass composition comprising the following glass ingredients: 60.2 to 70% by weight of SiO 2 ; 1 to 20% by weight of Al 2 O 3 ; B 2 O 3 , wherein the B 2 O 3 is present in an amount up to 10%; SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 61.2 to 90% by weight; a total of 3.0 to 15% by weight of R 2 O compounds, where R=Li, Na, and K, wherein the following condition is fulfilled: 0.1% ≦Na 2 O<6%; a total of 2.0 to 15% by weight of R′O compounds, where R′=Mg, and Zn; and a total of 1.0 to 20% by weight of MOx (TiO 2 +ZrO 2 +Ln x O y ), where Ln x O y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y 2 O 3 , Nb 2 O 5 , and Ta 2 O 5 , wherein the glass composition does not include CaO and the following condition is fulfilled: 0.070<(total content of R′O compounds)/(SiO 2 +Al 2 O 3 +B 2 O 3 )<0.200.