Patent ID: 8563149

Claim:
Glass for a data storage medium substrate, which comprises, as represented by mol percentage based on the following oxides, from 55 to 70% of SiO 2 , from 2.5 to 9% of Al 2 O 3 , from 0 to 10% of MgO, from 0 to 7% of CaO, from 0.5 to 10% of SrO, from 0 to 12.5% of BaO, from 0 to 2.5% of TiO 2 , from 0.5 to 3.7% of ZrO 2 , from 0 to 2.5% of Li 2 O, from 0 to 8% of Na 2 O, from 2.5 to 8% of K 2 O and from 0.5 to 5% of La 2 O 3 , provided that Al 2 O 3 and ZrO 2 (Al 2 O 3 +ZrO 2 ): is at most 12%, and Li 2 O, Na 2 O and K 2 O (R 2 O): is at most 12%, and which glass has a glass transition temperature of at least 660° C.