Icosahedral particles of an Al-Mn alloy produced by gas evaporation

Small particles of icosahedral Al-Mn alloy have been produced by evaporation of Al and Mn metals in Ar gas and studied by electron microscopy. The quasicrystalline particles were spherical in shape, with diameters ranging from 500 to 3000 Å, and showed speckled contrast in bright-field images, characteristic of strain. Dark-field images revealed granular bright and dark areas of a few hundred angstroms. This appearance is common with that of the melt-spun samples and may be attributed to misorientations between the granular domains. Elongated domains of ∼50 Å in width and a few hundred angstroms in length, which are unique in the present sample and not observed in the melt-spun sample, were also found. The critical cooling rate for the quasicrystal formation of the Al-Mn alloy was found to be ${10}^5$ °C/sec.