Atomic model of anti-phase boundaries in a face-centred icosahedral Zn–Mg–Dyquasicrystal

Abstract

An atomic model in the physical space for an anti-phase boundary (APB) inthe ordered face-centred icosahedral Zn–Mg–Dy quasicrystal phase ispresented, based on a six-dimensional model suggested by Ishimasa andShimizu (2000 Mater. Sci. Eng. A 294–296 232, Ishimasa 2001 privatecommunication). The physical space atomic positions of the defectedstructure were used for the calculation of the corresponding exit-planewavefunction and high-resolution transmission electron microscopy images. Theanalysis of the defect by inverse Fourier transformation reveals that whensuperstructure reflection spots are used for back-transformation, then at theAPB, bright lattice fringes are found to turn into dark ones, and viceversa. When fundamental reflections are used, the APB is not visible. Thisphenomenon is the same as the corresponding experimental study recentlypublished by Heggen et al(2001a Phys. Rev. B 64 014202). Based on thisatomic model it is found that the APB perpendicular to a fivefold axis A5(APB-A5) is a non-conservative boundary, while the APB perpendicularto a pseudo-twofold axis A2P (APB-A2P) is a conservative one. Thisfact is consistent with the experimental observation (Heggen et al2002 J.Alloys Compounds 342 330) that the frequency of occurrence of APB-A5 is90% in the heat-treated samples compared with that in the deformedsamples (45%), while the frequency of occurrence of APB-A2P is 34% in thedeformed samples compared with that in the heat-treated samples.