A structural model of the orthorhombic Al3Co derived from the monoclinic Al13Co4by high-resolution electron microscopy

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Abstract
A structural model of the orthorhombic approximant Al3Co of the Al-Co decagonal quasicrystal has been derived from the monoclinic approximant Al13Co4 by high-resolution electron microscopy. In the [010] projected image, the bright image points correspond to the Co-atom pentagonal networks in these two phases, but the tessellation of pentagons in them is different. The structure of Al3Co can be obtained by introducing repeated (100) faults at the unit-cell level in Al13Co4. There are 78 Al and 24 Co atom sites (some A1 sites are only partially occupied) in a unit cell (a= 1.446 nm, b = 0.8156 nm and c= 1.236 nm) satisfying the symmetry of the Pnmn space group. This structure is also akin to that of the orthorhombic Al3Mn which has similar a and c parameters.