Ferroelectric polarization of tetragonal BiFeO3—an approach from DFT calculations for BiFeO3–BaTiO3 superlattices—

Abstract Density functional theory calculations are conducted for tetragonal BiFeO 3 –BaTiO 3 superlattices to investigate the influence of electronic structures on ferroelectric spontaneous polarization ( P s ). When the number of the perovskite unit cells in one layer ( N ) is decreased below 10, the P s starts to decrease from the volume-averaged one (50.9 μ C cm −2 ) and eventually becomes half at N = 1. In the BiFeO 3 cell ( N = ∞) with a large P s (73.3 μ C cm −2 ), a covalent bond arising from a Bi_6p-O_2p orbital interaction is extended through a Bi–O network and stereo-chemical lone-pair electrons of Bi are accommodated in the opposite direction of the polar c axis. In the superlattice with N = 1, the Bi–O network cannot be developed by the presence of Ba, and then the Bi–O bond becomes ionic. We show that the large P s of the BiFeO 3 cell originates from the Bi_6p-O_2p mixing superimposed on the stereo-chemical nature of the lone-pair electrons of Bi.