Structural,electronic and optical properties of Ilmenite ATiO3(A=Fe,Co, Ni)

Ilmenite-type ATiO₃ (A=Fe, Co, Ni) crystals have been investigated via Generalized Gradient Approximation (GGA) in the scheme of Revised Perdew-Burke-Ernzerhof (RPBE) using the first-principles method. The band structures, densities of states, bond orders and charge populations, optical properties including the dielectric function ε(ω), absorption coefficient I(ω), refractive index n(ω), extinction coefficient k(ω), electron energy loss function L(ω) and reflectivity function R(ω), are calculated. The results show that the GGA-optimized geometries agree well with the experimental data. FeTiO₃ has a direct band gap, but both CoTiO₃ and NiTiO₃ exhibit indirect band gap. The analysis for densities of states and atomic charge populations exhibits that TiO bonds possess the stronger covalent bonding strength than AO bonds. The calculated optical properties along 100], 010] and 001] as well as polycrystalline directions demonstrate the significant optical anisotropy parallel and perpendicular to c-axis for ATiO₃. Finally, the origins of main peaks for optical spectra are presented based on electron transitions. Theoretical insights into the microscopic intrinsic properties of ATiO₃ should provide fundamental investigations for further understanding the Ilmenite ATiO₃ materials and improving their practical applications.