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The title compound crystallizes with monoclinic symmetry. Its structure derives from the cubic AuBe 5 -type structure via the introduction of planar defects parallel to {hhh} which lead to a nearly orthogonal ≈7×7×6.5 supercell having the cell parameters a s = 48.961(20) Å, b s = 48.994(4) Å, c s = 45.643(4) Å, β = 91.24(1) • . A four-dimensional structural analysis reveals a quasi-linear modulation of the atomic positions and occupancies of ytterbium and copper along c s . On the basis of this result and the electron microscopy images, a threedimensional model of the superstructure was constructed in space group C2. The model contains 7448 atoms per unit cell which are distributed over 350 Yb sites and 1519 Cu sites. It has the overall composition YbCu 4.43 , contains short Yb-Yb distances, and is consistent with the chemical and physical properties.

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SUMMARY Nb3Ge‐films synthesized on Mo‐substrates by the co‐evaporation method show a characteristic fabric with a quasi‐twelvefold symmetry around the [001]‐axis of the A15‐type cubic structure. Among approximate +30°‐ and ±60°‐rotation boundaries, grain boundaries having rotation angles between 28° and 29° are observed most frequently in the Nb3Ge‐films. Using the high resolution electron micrographs, a Σ17‐boundary having an ideal rotation angle of 28.07° is analysed and plausible boundary models on the atomic level are proposed.