Study of the structural, electronic, and optical properties of the host matrices of LiAl5O8 and LiGa5O8 via DFT

The structural, electronic, and optical properties of host matrices lithium aluminate spinel (LiAl5O8, LAO) and gallium lithium spinel (LiGa5O8, LGO) were analyzed based on calculations of the density functional theory. Optimizations of the crystal structures were performed using the generalized gradient approximation, while the electronic structure and optical properties were calculated using the modified Becke e Johnson potential. The calculated lattice parameters and atomic positions are in a good agreement with the experimental results. The calculated band gaps are indirect, Δ → Γ(LAO) and M → Γ(LGO), with values of 8.4 eV (LAO) and 5.6 eV (LGO); these are consistent with the experimental value of 8.5 eV for LAO. The electron transitions that generate the absorption edges of the compounds are well described by this work. Calculations of the refractive indices revealed the values of the static dielectric constants (zero frequency) of 1.50 (LAO) and 1.64 (LGO).