Regensburg 2004 – wissenschaftliches Programm
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M: Metallphysik
M 31: Quasikristalle II
M 31.6: Vortrag
Donnerstag, 11. März 2004, 17:45–18:00, H16
<100> chains of 2 n interpenetrated icosahedra in hexagonal Zn-Mg-RE (Y, Sm, Gd) phases — •D.W. Deng 1,2, K.H. Kuo2, M. Feuerbacher1, and K. Urban1 — 1Institut für Festkörperforchung, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany — 2Beijing Laboratory of Electron Microscopy, Institute of Physics, Chinese Academy of Sciences, PO Box 603, 100080 Beijing, PR China
The crystal structure of the hexagonal Zn3MgY phase has been determined by single-crystal X-ray diffraction. The structural model, refined to a final R value of 0.047, has the composition Zn60.68Mg18.28Y21.04, a = 9.082(2) Å and c = 9.415(5) Å and the space group P63/mmc. The structure of Zn3MgY is characterized by a layer structure consisting of FP(FP)’ layers stacked along the c axis, where F and P denote flat and puckered layers, respectively, and (FP)’ is related to FP by a 63 screw. The Zn3 icosahedra, in the PFP’ layer block are fused into pairs in the <100> directions. At the same time, the hexagonal Zn3MgY phase is known to consist of 2 interpenetrated Zn icosahedra along <100> directions. This can be considered as the fundamental period (n = 1) of a series of 2n super-periodic icosahedral chains. The hexagonal S, M, and L or µ 3, µ 5, and µ 7 phases of larger a parameters are found to have super-periodic chains containing 2n = 4, 6, and 8, respectively, interpenetrated icosahedra in <100> directions. The estimated periodicity of this series of super-periodic 2n (n = 2, 3 and 4) interpenetrated icosahedral chain agrees with most cases of the experimental a parameter of the hexagonal S, M, and L or µ 3, µ 5, and µ 7 phases.