STRUCTURE OF AL3MN, AN ORTHORHOMBIC APPROXIMANT OF THE DECAGONAL QUASI-CRYSTAL

A structural model of the orthorhombic approximant Y-Al3Mn of the AlMn decagonal quasicrystal has been derived from another orthorhombic approximant pi-AlMn. There are 124 Al atoms and 32 Mn atoms, with a composition of Al3.88Mn, in a unit cell with a = 1.487 nm, b = 1.247 nm and c = 1.256 nm, satisfying the symmetry of the space group of Pnma (or Pn2(1)a after refinement made on single-crystal X-ray analysis). The calculated X-ray powder diffraction pattern agrees well with the experimental results. The high-resolution electron microscopy image of Y-Al3Mn has been correlated with the [010] structural projection along the pseudo-tenfold axis.