Ion exchangeable glasses having high fracture toughness

A glass-based article, comprising:

• a compressive stress layer extending from a surface of the glass-based article to a depth of compression;
• a central tension region;
• and
• a composition at a center of the glass-based article comprising:
• greater than or equal to 45 mol % to less than or equal to 70 mol % SiO2;
• greater than or equal to 4 mol % to less than or equal to 25 mol % Al2O3;
• greater than or equal to 5 mol % to less than or equal to 20 mol % Li2O;
• greater than or equal to 0.1 mol % to less than or equal to 10 mol % Na2O;
• greater than or equal to 13 mol % to less than or equal to 25 mol % MgO;
• greater than or equal to 0.1 mol % to less than or equal to 4 mol % ZrO2;
• and
• greater than or equal to 0.1 mol % to less than or equal to 5 mol % K2O;
• wherein the glass has a KIC fracture toughness greater than or equal to 0.83 MPa·m0.5 and a Young's modulus greater than or equal to 86 GPa, and
• wherein (Li2O+Na2O+MgO)/Al2O3 is greater than or equal to 1.68 and less than or equal to 2.5, where each component concentration is in mol %.