| 摘要 |
A glass substrate for use as the substrate of an information recording medium such as a magnetic disk, magneto-optical disk, DVD, or MD or of an optical communication device, and a glass composition for making such a glass substrate, contains the following glass ingredients: 45 to 75% by weight of SiO<SUB>2</SUB>; 1 to 20% by weight of Al<SUB>2</SUB>O<SUB>3</SUB>; 0 to 8% by weight, zero inclusive, of B<SUB>2</SUB>O<SUB>3</SUB>; SiO<SUB>2</SUB>+Al<SUB>2</SUB>O<SUB>3</SUB>+B<SUB>2</SUB>O<SUB>3 </SUB>accounting for 60 to 90% by weight; a total of 0 to 20% by weight, zero inclusive, of R<SUB>2</SUB>O compounds, where R=Li, Na, and K; and a total of 0 to 15% by weight, zero inclusive, of TiO<SUB>2</SUB>+ZrO<SUB>2</SUB>+Ln<SUB>x</SUB>O<SUB>y</SUB>, where Ln<SUB>x</SUB>O<SUB>y </SUB>represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y<SUB>2</SUB>O<SUB>3</SUB>, Nb<SUB>2</SUB>O<SUB>5</SUB>, and Ta<SUB>2</SUB>O<SUB>5</SUB>.
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