Short-range order and the electronic structure of decagonal Al–Ni–Co

Detailed investigations of the atomic and electronic structures of decagonal Al–Ni–Co alloys have been performed. The topology of the structural model has been refined on the basis of the existing X-ray diffraction data. The chemical order on the decagonal lattice has been optimized via the comparison of the calculated electronic spectra with photoemission and soft-X-ray data and using total-energy calculations. The electronic structure calculations for large periodic approximants with up to 1276 atoms/cell have been performed self-consistently using a real-space tight-binding linear-muffin-tin orbital technique. The best agreement with the experimental spectra is achieved for a model with the innermost ring of the pentagonal columnar clusters occupied by Ni-atoms only. This configuration also has the lowest total energy. As in decagonal Al–Cu–Co we find a high density of states at the Fermi level, but the chemical ordering is very different: whereas in d-Al–Cu–Co direct Cu–Cu neighbours are suppressed and there is a slight preference for Co–Co homocoordination, in d-Al–Ni–Co a strong Ni–Ni interaction stabilizes the innermost Ni-ring, direct Co–Co neighbours are suppressed and there is a strong Co–Al interaction.