Eur. Phys. J. B 6, 25-32 (1998)
https://doi.org/10.1007/s100510050522

Al-Cu approximants in the Al₃C_u4 alloy^*

¹ State Key Laboratory for Materials Modification by Laser, Ion and Electron Beams, Dalian University Technology, Dalian, 116024, P.R. China
² Department of Materials Engineering, Dalian University of Technology, Dalian 116024, P.R. China
³ Atomic Imaging of Solids, Institute of Metals Research, Academia Sinica, Shenyang 110015, P.R. China

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Received: 8 July 1997
Revised: 19 May 1998
Accepted: 16 June 1998
Published online: 15 November 1998

Abstract

The Al₃C_u4 composition, with an e/a ratio of 1.86 being close to ternary Al-Cu-TM (Transition Metal) quasicrystals, has been chosen for the search of Al-Cu approximants. Phase structures and compositions were studied using TEM, X-ray diffraction and EPMA techniques. Two new phases were found: face-centered orthorhombic oF-Al_43.2Cu_56.8 (, , nm) and body-centered orthorhombic oI-Al_41.3Cu_58.7 (oI, , , nm). Their e/a ratios are the same as that of the Al-Cu-Fe icosahedral quasicrystal. Their space groups are probably oF-Fmm2 and oI-Imm2. Both are B2 vacancy-containing superstructures; unit cell compositions can be expressed approximately as oF-Al₃₆Cu and oI-Al₈Cu (: vacancies). They both exist in twinning variants of the types and . Such twinning modes indicate that these orthorhombic phases are the decomposition products of a high-temperature parent phase ε2-Al₂Cu₃, the atomic structure of which contains pentagonal atomic arrangements. Therefore the oF, oI, and phases are all B2-based approximants corresponding to the Al-Cu-TM quasicrystals.