Structural and electronic properties of cubic BiFeO3 from first-principles calculations

Based on density functional theory (DFT), the crystal structural and electronic properties of two cubic BiFeO3 phases (Fd 3‾ m-BiFeO3 and Pm 3‾ m-BiFeO3) have been researched. Using USPEX based on ab initio evolutionary algorithm, the cubic crystal structure (Fd 3‾ m) was predicted at ambient pressure. The structural parameters of the ambient-pressure cubic phase Fd 3‾ m and the high-temperature cubic phase Pm 3‾ m are given in the paper. Through the calculation of phonon dispersion curves, it is found that the Fd 3‾ m phase has no imaginary frequency and can exist stably at ambient pressure. However, the Pm 3‾ m phase has imaginary frequency and cannot exist stably at ambient pressure. In electronic band structures, the finite value at the Fermi level are suggestive of the metallicity of Fd 3‾ m and Pm 3‾ m phases, in which the highest valence band overlap with the lowest conduction band. It is concluded that two cubic phases of BiFeO3 are metal phases, which are different from the semiconductor properties of all BiFeO3 isomers previously reported. Their Partial Density of States diagrams show that Bi-6p, Fe-3d and O-2p have obvious hybridization in the range of −5 eV – 5 eV. Besides, we researched their charge transfer and charge localization. Finally, we calculated their elastic properties and found that Fd 3‾ m-BiFeO3 has higher Vickers hardness, which can extend the life of BiFeO3 devices. This work provides a solid theoretical guidance for understanding the electronic structure of multiferroic materials.