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

Detailed investigations of the atomic and electronic structures of decagona l 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 comparis on of the calculated electronic spectra with photoemission and soft-X-ray d ata and using total-energy calculations. The electronic structure calculati ons for large periodic approximants with up to 1276 atoms/cell have been pe rformed self-consistently using a real-space tight-binding linear-muffin-ti n orbital technique. The best agreement with the experimental spectra is ac hieved for a model with the innermost ring of the pentagonal columnar clust ers 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 F ermi level, but the chemical orderings is very different: whereas in d-Al-C u-Co direct Cu-Cu neighbours are suppressed and there is a slight preferenc e for Go-Co homocoordination, in d-Al-Ni-Co a strong Ni-Ni interaction stab ilizes the innermost Ni-ring, direct Go-Co neighbours are suppressed and th ere is a strong Co-Al interaction. (C) 2000 Published by Elsevier Science B .V.