Structural complexity of the intermetallic compound o-Al13Co4

Abstract The crystal structure of the complex intermetallic phase o-Al13Co4 was first investigated in 1994, but some open questions still remained. The new refinement of the crystal structure using high-resolution X-ray diffraction data resulted in a much more complex model including a large number of split positions (space group Pnm21, a = 8.1590(6) A, b = 12.349(1) A, c = 14.453(1) A). The model is interpreted in terms of local violation of the translational symmetry, which is confirmed by HRTEM and HRSTEM investigations. Chemical bonding between two partial structures in o-Al13Co4 - three-dimensional framework and linear Co–Al–Co groups in cages of the latter – along with the stacking faults (local twinning) are discussed as possible reasons for such an extended disorder.