First-principles study of structural phase transition, elastic and electronic properties of BaTiO₃ under pressure

The structural phase transition, elastic and electronic properties of BaTiO₃ for both orthorhombic and rhombohedral phases have been investigated by the generalized gradient approximation in the framework of density-functional theory. The calculated lattice parameters at the ground state are found to be in good agreement with the available experimental data and seem to be better than other calculated results. The calculated transition pressure of BaTiO₃ at 0 K between the two phases is 5.8 GPa, which agrees with other theoretical value 5.4 GPa. The calculated elastic constants C_ij of these two phases have some deviations with the experimental and theoretical results, but they, generally, conform to them well. From the calculated elastic constants C_ij, the bulk-modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ, shear sound velocity V_S, longitudinal sound velocity V_L of the two phases are successfully obtained. The calculated bulk-modulus of these two phases are found to be in good agreement with other theoretical results. We calculated elastic anisotropy and presented the direction-dependent linear compressibility for both phases to display the elastic anisotropy more visually. Our calculations indicate that the orthorhombic and rhombohedral phases of BaTiO₃ both are indirect-gap semiconductor with gap value of 2.087 and 2.240 eV, respectively, close to previous theoretical results. Combined with the density of states, the characteristics of the band structure have been analyzed and their origins have been specified. (author)