First-principles investigations into the characteristic properties of corundum samples from the Arusha region

Understanding the characteristic properties of corundum gemstone is essential for its use in gemstone treatment, as well as in various other industries. Corundum samples obtained from the Arusha mining region were analyzed for crystallographic data using XRD analysis. This crystallographic data is then utilized to construct the crystal structure of the samples in the Biovia Materials Studio modeling and simulation software. The electronic, optical, and elastic properties of the selected sample are explored using the plane wave approach within the framework of the first-principles density functional theory (DFT), implying the Cambridge Serial Total Energy Package (CASTEP) code with Generalized Gradient Approximations and the Perdew-Burke-Ernzerhof exchange-correlation functional. For the calculations, a sampling mesh of 6×6×2 k-points, with the cut-off energy of 600 eV, and the total energy convergence within 1.0 x 10-5 eV/atom is used. The band gap determined is 6.13 eV at the gamma point which is in concurrence with the previous values from the literature. The polarized optical properties of the structure were studied and visualized by plotting their directional dependencies. The reflectivity spectra exhibited isotropic behavior in the ultraviolet range with a maximum peak at 52.24 nm along [001], [010], and [100] directions. Also, the absorption peak is observed around 65.59 nm along [001], [010], and [100] directions. Pugh’s ratio suggests that the sample is deemed brittle with a ratio of 0.65 as G/B > 0.5. The calculated Poisson’s ratio is 0.23 indicating the dominant covalent bond. The results indicate that the investigated sample is a suitable insulator, brittle, and displays isotropic optical reflectivity.