Chemical order in an Al-Pd-Mn icosahedral quasicrystal

The icosahedral structure of Al₇₀Pd₂₀Mn₁₀and Al₆₅Cu₂₀Fe₁₅quasicrystals in rapidly solidified and annealed states has been examined by electron and X-ray diffraction techniques. Broadening and distortion of the diffraction peaks due to atomic disordering were observed in rapidly solidified Al₆₅Cu₂₀Fe₁₅, but were not observed in rapidly solidified Al₇₀Pd₂₀Mn₁₀. The rapidly solidified Al₇₀Pd₂₀Mn₁₀quasicrystal has a highly ordered atomic arrangement which is nearly the same as that for an Al₆₅Cu₂₀Fe₁₅quasicrystal annealed at a temperature just below the melting point. On the basis of the thermodynamical data, it is presumed that a strong chemical order(bonding) between Pd and A1 or Mn prevents the Al₇₀Pd₂₀Mn₁₀quasicrystal from generating atomic disordering and phason strains during rapid solidification.