Exploration in the Sc-Al-Cu system: evidence for i-ScAl2.4Cu3.2 quasicrystal and new crystal data for five intermetallic phases

摘要

The ternary system Sc-Al-Cu system has been investigated in this work. Several alloys with various compositions have been prepared by arc-melting from the elements and studied by Xray diffraction. An icosahedral quasicrystal of formula ScAl_(2.4)Cu_(3.2) has been identified using the reciprocal space reconstructed from its diffraction images. The diffraction data collected for several single crystals led to solve and refine five crystal structures: cubic ScAlCu_2 (Fm3m), hexagonal ScAl_(1.1)Cu_(0.9) (P6m2), hexagonal ScAl_(2.4)Cu_(2.9) (P6_3/ mmc), tetragonal ScAl_(5.3)Cu_(6.7) (I4/mmm) and orthorhombic ScAl_(2.2)Cu_(3.4) (Cmmm). Almost all these structures are characterised with copper/aluminum atomic mixing at most of the crystallographic sites and the atomic arrangements are favourable to the existence of stoichiometry ranges for the compounds. These results, providing new single crystal data sets for these ternary compounds, clarify and confirm the structures previously reported (from crystal or powder data).