Direct imaging of the distortions of MnO6 octahedra in La0.4Ca2.6Mn2O7

The distortions of MnO6 octahedra in layered manganites La0.4Ca2.6Mn2O7, which play a key role in the structure transformations and physical properties, were investigated by using a 200 kV high-resolution transmission electron microscope. Tetragonal, orthorhombic (superstructure), and monoclinic phases were found to coexist in the form of microdomains. In particular, the distortions of MnO6 octahedra in the orthorhombic and monoclinic phases were revealed directly at atomic resolution by means of image deconvolution. The differences of the Mn atomic columns in position, size, and contrast among the tetragonal, orthorhombic, and monoclinic phases, caused by the rotation or tilt of the MnO6 octahedra, were directly obtained from the corresponding structure projection maps.