structure of a W-(AlCoNi) crystalline phase related to Al-Co-Ni decagonal quasicrystals, studied by single crystal X-ray diffraction

摘要

The crystal structure of a W-(AlCoNi) phase, which is closely related to Al-Co-Ni decagonal quasicrystals, has been studied by the single crystal X-ray diffraction. The W-(AlCoNi) phase was obtained from an Al_(72.5)Co_(20)Ni_(7.5) alloy sample annealed at 950 deg C and its structure indicates the space group Cm (No. 8) with lattice parameters a = 39.668(3) A, b = 8.158(1) A, c = 23.392(1) A and beta = 90.05(1) deg. A structural model with R(F) less than 0.087 for the observed 16 200 reflections can reproduce contrasts of atomic scale images obtained by high-angle annular detector dark-field scanning transmission electron microscopy together with high-resolution electron microscopy. The structure of the W-(AlCoNi)phase provides a fundamental atomic arrangement for the columnar atom cluster observed commonly in the Al-Co-Ni decagonal quasicrystals, and makes it possible to derive a structural model for the structures of the Al-Co-Ni decagonal quasicrystals.