Atomic Short-Range Order in an Al72Ni20Co8 Decagonal Quasicrystal by Anomalous-X-Ray Scattering

Hiroshi ABE, Yoshie MATSUO1, Hiroyuki SAITOH2, Tomoko KUSAWAKE2, Ken-ichi OHSHIMA2 and Hironori NAKAO3

Department of Materials Science and Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan
1Department of Physics, Nara Women's University, Kitauoya-Higasi, Nara 630-8506, Japan
2Institute of Materials Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba 305-8573, Japan
3Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba 305-0801, Japan

Jpn. J. Appl. Phys.  Vol.39 (2000)  No.11A  pp.L1111 - L1114

    By anomalous-X-ray scattering, the diffuse scattering around Bragg reflections was observed in a single decagonal quasicrystal of Al72Ni20Co8, which has no phason strain. The diffuse scattering is distributed around the center of the superstructure points. Intensity modulations of the diffuse scattering occur at each incident wavelength. The contrast of diffuse scattering shows the presence of atomic short-range order (SRO) in three kinds of pair correlation functions: between Al and Ni, between Ni and Co and between Co and Al. The correlation length of the diffuse scattering is estimated to be 22.5 A.

KEYWORDS: ideal decagonal quasicrystal, 3 wavelength method, atomic short-range order, no phason strain


FIG.1 

Reciprocal space perpendicular to the periodic direction of the decagonal Al72Ni20Co8. The area of the spot is proportional to the intensity of reflections. The diffuse scattering has been measured around the labeled reflections.. 
FIG.2 

Diffuse scattering on the quasiperiodic plane (Qx, Qy) around (a) 10-3-30 , (b) 30-4-40  and (c) 1-2-5-40  at 8.304 keV, where each interval of contour maps is 5 electron units per atom. The raveled reflections of A, B and C in Fig.1 stand for 10-3-30, 30-4-40  and 1-2-5-40 . The white crosses on broad peaks exhibit the positions of superstructure reflections. Other sharp peaks are main reflections. Line A in Fig. 2(b) is a measurement region in Fig. 4(a). Dot B in Fig. 2(b) is used for the calculated values in Table I. 

FIG.3 

FWHM of Bragg reflections along | Gperp|. Open circles are FWHM of Al70Ni15Co15 and closed circles are that of Al72Ni20Co8. FWHM values are deconvoluted by the experimental resolution function.
Fig. 4 

(a) Line-scan along Qy in line A of Fig 2(b) around the   Bragg reflection. Open squares, open circles and closed triangles are diffuse intensities at 8.304, 8.098 and 7.686 keV, respectively. (b) Three kinds of pair-correlation functions, aAl,Ni(Q), aNi,Co(Q) and aCo,Al(Q), in Laue units per atom at the same Q region.

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Department of Materials Science and Engineering
National Defense Academy

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