Planar defect in approximant: the case of Cu-Al-Sc alloy

The {110} planar defect formed in the Cu-Al-Sc 1/1 approximant has been studied by means of electron microscopy and 6-dimensional analysis. As the displacement vector of the planar defect, 1/2 <{\tau}, 1/{\tau}, 0> has been proposed. Here {\tau} denotes the golden ratio. This vector corresponds to a 6-dimensional translation of type [111000] and also to the c-linkage of Tsai-type clusters. An atomic structure model of the planar defect has been constructed referring to the structural properties of the regular 1/1 approximant; namely truncated triacontahedron framework and embedded clusters. This structural model was validated by the agreement between the observed and simulated HAADF-STEM images. Models of the intersection of two planar defects and the triple point, where three planar defects intersect, were also proposed. All local structures formed at these defects are understood by the concept of so-called canonical cell tiling.