Electronic and elastic properties of the tetragonal anatase TiO2 structure from first principle calculation

Based on the density functional theory (DFT), the band structure, density of state and elastic constants of anatase TiO2 were studied and analyzed by using the Cambridge Sequential Total Energy Package (CASTEP) package. Besides, the mechanical properties, Debye temperature and the tendency of the preferential growth of anatase TiO2 are also studied. The results show that (1) anatase TiO2 is indirect band gap semiconducting, with a energy gap of 2.116 eV and an obvious electron transfer phenomenon between Ti and O, where the electron distribution has strong localization. (3) Ti-O bond also shows some covalent bond characteristics due to the existence of hybridization. (3) the bulk modulus of elasticity is estimated to be 177.24 GPa, higher than the shear modulus of 42.69 GPa and Young's modulus of 118.54 GPa, showing great anisotropic characteristics. (4) the nanocrystal growth preferentially grows in the edge of the [101] direction in anatase TiO2 structure. As there is less slip system in TiO2 ,the lack of gliding planes of anatase TiO2 makes it easily to be broken by fracture. The anatase TiO2 has the brittle fracture and poor toughness. As the shear modulus is relatively small, in the anatase TiO2 tetragonal system, this kind of hybrid network structure of ionic bond and covalent bond makes this material show a greater anisotropy.