MANGANESE-INDUCED ORDERING IN THE ALPHA-(AL-MN-FE-SI) APPROXIMANT PHASE

We report a transmission electron microscopy study of alpha-(Al-Mn-Fe- Si) phases, isostructural to the alpha-(Al-Mn-Si) approximant phase. S elected-area diffraction patterns exhibit a noticeable diffuse scatter ing due to short-range ordering. We show that the ordering effect is r einforced by the Mn additions. This diffuse scattering can be describe d by a surface close to a polyhedron in the reciprocal space. We inter pret the shape of this surface as a consequence of the ordering of two types of entities (Mackay icosahedra) along the [111] directions.