To provide An Al.sub.2O.sub.3-free dental lithium silicate glass composition comprising the following components: SiO.sub.2: 60.0 to 80.0% by weight Li.sub.2O: 10.0 to 17.0% by weight K.sub.2O: 0.5 to 10.0% by weight a nucleating agent: 1.0 to 6.0% by weight a colorant: 0.0 to 10.0% by weight, and, a metal oxide Me(tetravalent)O.sub.2: 5.0 to 10.0% by weight.

ZrO.sub.2-toughened glass ceramics having high molar fractions of tetragonal ZrO.sub.2 and fracture toughness value of greater than 1.8 MPa.Math.m.sup.1/2. The glass ceramic may also include also contain other secondary phases, including lithium silicates, that may be beneficial for toughening or for strengthening through an ion exchange process. Additional second phases may also decrease the coefficient of thermal expansion of the glass ceramic. A method of making such glass ceramics is also provided.

A glass-ceramic includes glass and crystalline phases, where the crystalline phase includes non-stoichiometric suboxides of titanium, forming ‘bronze’-type solid state defect structures in which vacancies are occupied with dopant cations.

A glass-ceramic includes a silicate-containing glass and crystals within the silicate-containing glass. The crystals include non-stoichiometric tungsten and/or molybdenum sub-oxides, and the crystals are intercalated with dopant cations.

The invention relates to glass articles suitable for use as electronic device housing/cover glass which comprise a glass ceramic material. Particularly, a cover glass comprising an ion-exchanged glass ceramic exhibiting the following attributes (1) optical transparency, as defined by greater than 90% transmission at 400-750 nm; (2) a fracture toughness of greater than 0.6 MPa.Math.m.sup.1/2; (3) a 4-point bend strength of greater than 350 MPa; (4) a Vickers hardness of at least 450 kgf/mm.sup.2 and a Vickers median/radial crack initiation threshold of at least 5 kgf; (5) a Young's Modulus ranging between about 50 to 100 GPa; (6) a thermal conductivity of less than 2.0 W/m C., and (7) and at least one of the following attributes: (i) a compressive surface layer having a depth of layer (DOL) greater and a compressive stress greater than 400 MPa, or, (ii) a central tension of more than 20 MPa.

Embodiments of the present disclosure pertain to crystallizable glasses and glass-ceramics that exhibit a black color and are opaque. In one or more embodiments, the crystallizable glasses and glass-ceramics include a precursor glass composition that exhibits a liquidus viscosity of greater than about 20 kPa*s. The glass-ceramics exhibit less than about 20 wt % of one or more crystalline phases, which can include a plurality of crystallites in the Fe.sub.2O.sub.3TiO.sub.2MgO system and an area fraction of less than about 15%. Exemplary compositions used in the crystallizable glasses and glass-ceramics include, in mol %, SiO.sub.2 in the range from about 50 to about 76, Al.sub.2O.sub.3 in the range from about 4 to about 25, P.sub.2O.sub.5+B.sub.2O.sub.3 in the range from about 0 to about 14, R.sub.2O in the range from about 2 to about 20, one or more nucleating agents in the range from about 0 to about 5, and RO in the range from about 0 to about 20.

Glass-ceramics exhibiting a Vickers indentation crack initiation threshold of at least 15 kgf are disclosed. These glass-ceramics may be ion exchangeable or ion exchanged. The glass-ceramics include a crystalline and amorphous phases generated by subjecting a thin precursor glass article to ceramming cycle having an average cooling rate in the range from about 10 C./minute to about 25 C./minute. In one or more embodiments, the crystalline phase may comprise at least 20 wt % of the glass-ceramics. The glass-ceramics may include -spodumene ss as the predominant crystalline phase and may exhibit an opacityabout 85% over the wavelength range of 400-700 nm for an about 0.8 mm thickness and colors an observer angle of 10 and a CIE illuminant F02 determined with specular reflectance included of a* between 3 and +3, b* between 6 and +6, and L* between 88 and 97.

A glass-ceramic includes a silicate-containing glass and crystals within the silicate-containing glass. The crystals include non-stoichiometric tungsten and/or molybdenum sub-oxides, and the crystals are intercalated with dopant cations.

Disclosed herein are glass-ceramics having crystalline phases including -spodumene ss and either (i) pseudobrookite or (ii) vanadium or vanadium containing compounds so as to be colored and opaque glass-ceramics having coordinates, determined from total reflectancespecular includedmeasurements, in the CIELAB color space of the following ranges: L*=from about 20 to about 45; a*=from about 2 to about +2; and b*=from about 12 to about +1. Such CIELAB color space coordinates can be substantially uniform throughout the glass-ceramics. In each of the proceeding, -quartz ss can be substantially absent from the crystalline phases. If present, -quartz ss can be less than about 20 wt % or, alternatively, less than about 15 wt % of the crystalline phases. Also Further crystalline phases might include spinel ss (e.g., hercynite and/or gahnite-hercynite ss), rutile, magnesium zinc phosphate, or spinel ss (e.g., hercynite and/or gahnite-hercynite ss) and rutile.

A glass-ceramic includes glass and crystalline phases, where the crystalline phase includes non-stoichiometric suboxides of titanium, forming bronze-type solid state defect structures in which vacancies are occupied with dopant cations.