CHEMICAL EFFECTS ON PERIODICITY AND STRUCTURE OF DECAGONAL PHASES IN AL-NI-BASED AND AL-CO-BASED ALLOYS

The structures of decagonal phases in binary Al-Ni and Al-Co systems and ternary Al70NixTM1-x(TM = Co, Rh or Ir) alloys have been studied by electron diffraction. In the Al-Co system, the periodicity of the decagonal phase is 1.6 nm in Al80Co20, and 0.8 nm in Al76.5Co23.5 and Al72Co28, suggesting that the stacking rule between Al and Co atoms is different along the c axis for the three alloys. In the ternary systems, diffuse streaks and periodicity systematically vary with the atom substitution of Co for Ni and Ir for Ni, indicating that Ni, Co and Ir atoms play different roles in the decagonal phase and exhibit various sorts of chemical order with Al atoms.