A LEED comparison of structural stabilities of the three high-symmetry surfaces of Al-Pd-Mn bulk quasicrystals

It is shown that low-energy electron diffraction (LEED) patterns of the thr ee high-symmetry surfaces (fivefold, threefold and twofold) of icosahedral Al-Pd-Mn are all compatible with quasicrystallinity, under specific conditi ons of preparation. This conclusion results from comparing symmetries of ex perimental surface LEED patterns with bulk X-ray diffraction data which are converted to the conditions of the LEED experiment. This conclusion is als o based upon an analysis of relative diffraction spot spacings in LEED. Hen ce, none of the three surfaces exhibits a massive lateral reconstruction, i .e. massive deviation from quasicrystallinity. The LEED pattern of the five fold surface is distinct from the LEED pattern of the pseudo-tenfold surfac e of an orthorhombic approximant. We believe that this rules out the possib ility that the fivefold surface of the icosahedral quasicrystal reconstruct s to an approximant with tenfold or pseudo-10-fold symmetry. The twofold an d threefold surfaces facet more readily, indicating qualitatively that they are less stable than the fivefold surface. (C) 2000 Elsevier Science B.V. All rights reserved.