DO QUASI-CRYSTALS EXIST IN THE MN-AL SYSTEM

We have investigated a number of Mn-Al alloys (of different compositions) obtained by rapidly quenching from the liquid state or by annealing at different temperatures, in order to determine whether quasi-crystals with odd symmetry, giving rise to powder diffraction patterns non-indexable by conventional crystallographic methods, really do exist. We state that the powder diffraction pattern of the 'quasi-crystalline' phase of the Mn-Al system may be well indexed by conventional crystallography. Therefore, the five- or ten-fold symmetries observed in the electron diffraction patterns of the Mn-Al phase can only be due to twinning. The real crystal symmetry obeys the laws of conventional crystallography.