Disorder in Al-Li-Cu and Al-Mn-Si Icosahedral Alloys

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Science  30 Oct 1987:
Vol. 238, Issue 4827, pp. 660-663
DOI: 10.1126/science.238.4827.660


Faceted dendrites of icosahedral AL6Li3Cu have been studied by high-resolution x-ray scattering. The samples display long-range icosahedral symmetry both in their diffraction patterns and in their macroscopic morphology. Despite the appearance of well-defined facets, the samples have a high degree of atomic disorder. The Bragg peaks have symmetry-dependent shapes and widths that scale linearly with G⊥ (phason momentum). The peak widths are surprisingly similar to those found in icosahedral Al-Mn-Si alloys in both their absolute magnitude and their dependence on G⊥. The origin of these features in models for the icosahedral phase is discussed.