Provided herein are glass based articles comprising SiO2, Al2O3, and two or more metal oxides selected from the group consisting of La2O3, BaO, Ta2O5, Y2O3, and HfO2. The glass based articles typically are characterized by a high fracture toughness (e.g., at least 0.86 MPa*m0.5), a high Young's modulus value (e.g., at least 85 GPa) and/or a stress optical coefficient (SOC) of not more than 3 Brewster (e.g., about 1.3 Brewster to about 2 Brewster). Also provided herein are glass based articles comprising SiO2 and two or more of MxOy, wherein M is Ba, La, Ta, Y, Al or Hf; wherein the total amount of SiO2 is the same or substantially the same as that of a reference glass based article comprising two or more binary compositions of MxOy—SiO2, wherein the reference glass based article has the same molar percentage of each MxOy, and the molar ratio of MxOy to SiO2 in each binary composition is 4/(c*x), wherein c is the number of charges of M.