Theoretical predictions of composition-dependent structure and properties of alumina-rich spinel

Alumina-rich spinel (MgO·nAl2O3, n ≥ 1) was described as a solid solution of MgAl2O4 and Al8/3O4 (γ-Al2O3) with formula of Mg1–xAl2(1+x/3)O4 (0 ≤ x ≤ 1). Five redefined supercell models of MgO·nAl2O3 were constructed to investigate the composition-dependence of structural, electronic, optical and mechanical properties. The first-principles calculations were developed with high accuracy to evaluate the lattice constant, electronic structure, dielectric function and elastic constants. The detailed structural information was presented by analyzing the variations in lattice constant, interstitial volume and anion parameter with the content of γ-Al2O3. The composition-dependent bulk modulus, shear modulus and electronic structure of alumina-rich spinel were well discussed. As increased the content of Al, the mechanical properties showed an increasing trend, while the optical absorption in the UV region presented a blue-shift of ∼1.2 eV. These theoretical results provided a basis for understanding the crystal structure and intrinsic properties of alumina-rich spinel.