The Crystalline Structure of O-AlFePd

抄録

The structure of O-AlFePd has been analyzed by single-crystal X-ray diffraction, yielding space group Cmca (No. 64), a = 0.8130(1) nm, b = 1.5474(2) nm, c = 2.3868(4) nm, atoms/cell = 204, F(000) = 3339, D_calc = 5.621 Mg m⁻³ and R = 0.0294 for the 2117 observed reflections with F_obs > 4.0σ(F_obs). The structure consists of four Fe sites, one Fe/Pd mixed site, and fifteen Al sites, and the corresponding structural formula is Al₁₃(Fe,Pd)₄ (Z = 8). The O-AlFePd phase is a new type of approximant of decagonal quasicrystals with a periodicity of 0.8 nm, and the alternation of flat and puckered layers at an interval of about 0.2 nm is the fundamental structural feature. The structure could be also described by a linkage of pentagonal atom columns similar to that found in monoclinic Al₁₃Fe₄. Nevertheless, the columnar linkage for the O-AlFePd phase is unique, and this allows us to advance an idea explaining the fine (001) glide twins frequently found in the Al₁₃Fe₄ phase.