Elucidation of crystal and electronic structures within highly strained BiFeO 3 by transmission electron microscopy and first-principles simulation

Crystal and electronic structures of ∼380 nm BiFeO₃ film grown on LaAlO₃ substrate are comprehensively studied using advanced transmission electron microscopy (TEM) technique combined with first-principles theory. Cross-sectional TEM images reveal the BiFeO₃ film consists of two zones with different crystal structures. While zone II turns out to have rhombohedral BiFeO₃, the crystal structure of zone I matches none of BiFeO₃ phases reported experimentally or predicted theoretically. Detailed electron diffraction analysis combined with first-principles calculation allows us to determine that zone I displays an orthorhombic-like monoclinic structure with space group of Cm (=8). The growth mechanism and electronic structure in zone I are further discussed in comparison with those of zone II. This study is the first to provide an experimentally validated complete crystallographic detail of a highly strained BiFeO₃ that includes the lattice parameter as well as the basis atom locations in the unit cell.