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Structural model of the orthorhombic non-Fibonacci approximant in the Al12Fe2Cr alloy

机译:Al12Fe2Cr合金中正交各向异性非斐波那契近似值的结构模型

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Al-5.103(Fe,Cr), orthorhombic, Imm2, a=12.34, b=12.41, c=30.71 Angstrom, V=4701 Angstrom(3), atoms/cell=305 (average), D-x similar or equal to 3.4 g cm(-3). A structural model of the non-Fibonacci approximant O-AlFeCr with composition Al-5.103(Fe,Cr) found in an Al12Fe2Cr alloy has been derived from its high-resolution electron microscopy images and the structure of the hexagonal mu-Al4Mn [Shoemaker, Keszler & Shoemaker (1989). Acta Cryst. B45, 13-20], being isostructural to mu-Al4Cr. Among the 14 unique positions of transition metal (TM) atoms, 13 are icosahedrally coordinated: five of these icosahedra interpenetrate into each other, forming icosahedral chains along [010], and the remaining eight icosahedra with their twofold axis parallel to this axis. This structural model describes a (010) layer structure with a sequence (PFP)-F-m((PFP)-F-m)(I), where a flat layer F (a mirror plane) is sandwiched between two puckered P and P-m layers, and ((PFP)-F-m)(I) is related to (PFP)-F-m through a body-centred translation. The interatomic distances are 2.51-2.74 Angstrom for TM-TM, 2.38-2.99 for TM-Al and 2.41-3.18 Angstrom for Al-Al. Simulated images and electron diffraction patterns calculated based on this structural model are comparable with the experimentally observed results.
机译:Al-5.103(Fe,Cr),斜方晶,Imm2,a = 12.34,b = 12.41,c = 30.71埃,V = 4701埃(3),原子/晶胞= 305(平均),Dx等于或等于3.4 g厘米(-3)。在Al12Fe2Cr合金中发现的具有成分为Al-5.103(Fe,Cr)的非斐波那契近似O-AlFeCr的结构模型是由其高分辨率电子显微镜图像和六角形mu-Al4Mn的结构得出的。 Keszler&Shoemaker(1989)。 Acta Cryst。 B45,13-20],与mu-Al4Cr同构。在过渡金属(TM)原子的14个唯一位置中,有13个二十面体配位:这些二十面体相互渗透,沿着[010]形成二十面体链,其余八个二十面体的双轴平行于该轴。该结构模型描述了具有序列(PFP)-Fm((PFP)-Fm)(I)的(010)层结构,其中平层F(镜面)夹在两个褶皱的P和Pm层之间,并且((PFP)-Fm)(I)通过以身体为中心的翻译与(PFP)-Fm相关。 TM-TM的原子间距离为2.51-2.74埃,TM-Al的原子间距离为2.38-2.99,而Al-Al的原子间距离为2.41-3.18埃。基于该结构模型计算的模拟图像和电子衍射图谱与实验观察到的结果相当。

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