Real space crystallography of a complex metallic alloy: high-angle annular dark-field scanning transmission electron microscopy of o-Al4(Cr,Fe)

High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) has been performed along the low-index zone axes of the o-Al4(Cr,Fe) complex metallic alloy to obtain a real-space representation of the crystal structure and to elucidate the material's inherent structural disorder. By comparing experiments with multislice STEM simulations, the model previously suggested by X-ray diffraction is further refined to provide a new set of positions and occupancies for the transition metal atoms. Pmnb is suggested as the new space group for the o-Al4(Cr,Fe) phase. A nonperiodic layer-type modulation, averaged out in bulk diffraction methods, is detected, corroborating the need for complementing bulk diffraction analysis with real-space imaging to derive the true crystal structure of Al4(Cr,Fe).