Glass-ceramics for magnetic disc substrate, magnetic disc substrate and magnetic disc

Abstract

A novel Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 series glass-ceramics for magnetic disc substrate use, which can prevent deformation of the substrate at a large temperature change and provide a strong, small and compact magnetic disc substrate without trouble and much reading and/or writing informations on the smoothened surface of the substrate, is provided. The glass-ceramics has a main crystal phase of lithium disilicate (Li.sub.2 O.2SiO.sub.2) phase, the peak intensity I of cristobalite phase (CRI) of at least 20 but not more than 50 when the peak intensity of I of lithium disilicate (L2S) phase measured by an X-ray diffraction analysis is taken as 100, and containing 1.0-3.0 parts by weight of Cr.sub.2 O.sub.3 and 1.0-3.0 parts by weight of MnO when the sum of metal oxides other than Cr.sub.2 O.sub.3 and MnO is taken as 100 parts by weight.

Dependencies are inferred from the claim text.