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Keywords:

  • Intermetallic phases;
  • Alloys;
  • Germanides;
  • Electron Localization Function;
  • Structure elucidation

Abstract

The intermetallic compounds, CaNi5Ge3, Ca15Ni68Ge37, and Ca7Ni48.9(4)Ge22.1(4), were prepared by arc-melting of the elements and subsequent heating in welded tantalum ampoules. The compounds were investigated by powder and single-crystal X-ray diffraction methods. Each of the three compounds crystallized in a different structure type, namely, CaNi5Ge3 in the space group P4/mbm, a = 8.0855(1) Å, c = 7.8466(1) Å, wR2 = 0.054, 439 F2 values, 31 variable parameters; Ca15Ni68Ge37 in the space group Pequation image2m, a = 22.436(2) Å, c = 3.9684(4) Å, wR2 = 0.096, 1849 F2 values, 133 variable parameters; Ca7Ni48.9(4)Ge22.1(4) in the space group P6/mmm, a = 17.381(4) Å, c = 4.046(1) Å, wR2 = 0.082, 693 F2 values, 59 variable parameters. The crystal structures consist of complex 3D networks of nickel and germanium atoms that have common motifs, namely, different sections of the Ni3Ge structure, as well as, Ca-centered hexagonal prisms of Ni and Ge, which have been observed in the CaNi2Ge2 structure. As the Ca content decreases, the Ni-Ge substructures form one-, two-, and three-dimensional networks. The disorder in Ca7Ni48.9(4)Ge22.1(4) is explained by a structural frustration. The electronic structure and chemical bonding of CaNi5Ge3 is discussed by means of band-structure calculations.