Glasses and glass ceramics including a metal oxide concentration gradient

Embodiments of a glass-based article including a first surface and a second surface opposing the first surface defining a thickness (t) of about 3 millimeters or less (e.g., about 1 millimeter or less), and a stress profile, wherein all points of the stress profile between a thickness range from about 0•t up to 0.3•t and from greater than 0.7•t, comprise a tangent that is less than about -0.1 MPa/micrometers or greater than about 0.1 MPa/micrometers,, are disclosed. In some embodiments, the glass-based article includes a non-zero metal oxide concentration that varies along at least a portion of the thickness (e.g., 0•t to about 0.3•t). In some embodiments, the concentration of metal oxide or alkali metal oxide decreases from the first surface to a point between the first surface and the second surface and increases from the point to the second surface. The concentration of the metal oxide may be about 0.05 mol% or greater or about 0.5 mol% or greater throughout the thickness. Methods for forming such glass-based articles are also disclosed.