The decagonal phase in (Al, 1)₆₅co₂₀cu₁₅ alloys

The complete stereographic projection showing the prominent zone axes and Kikuchi bands of the 7-99 ± 0 07 Å periodic Al₆₅ -_xCo₂₀Cu₁₅Si_x decagonal phase, determined from tilting experiments using selected-area diffraction and convergent-beam diffraction, is presented. Important differences with the stereographic projection for the Al-Mn 12-4 Å periodic decagonal phase are emphasized. The zone axes are indexed using basis vectors that are constructed from distorted icosahedra. The appropriate distortion is determined from the stereographic projection. Unlike existing indexing schemes, only minor adjustments of the distortion are required to index successfully both the Al-Mn and the Al-Co-Cu-Si decagonal phases. A new atomic model is proposed and discussed in the light of these diffraction results.