Structure of a new multicomponent stannide and comments on the Yarmolyuk-Kripyakevich criterion for Frank-Kasper phases

Chem. Met. Alloys 7 (2014) 169-180

https://doi.org/10.30970/cma7.0289

Volodymyr Gvozdetskyi, Roman Gladyshevskii, Viktor Hlukhyy

The structure of a new stannide, Nb_4.4V_1.6Ni₆Sn_0.9, was refined from X-ray single-crystal diffraction data (P6₃/mmc, a = 4.9433(5), c = 17.935(3) Å). It appeared to be formed by two substructures: Nb₅Ni_6.84V_0.16Sn_0.84 and V₁₂Sn, in the approximate ratio 9:1. The first substructure, Nb₅Ni₆(Ni_0.84V_0.16)Sn_0.84, is an ordering variant of the Cs₆K₇ type and belongs to the family of tetrahedrally close-packed structures, in which the atoms are surrounded by P- (16 vertices), Q- (15 vertices), R- (14 vertices), and X- (12 vertices) Frank-Kasper polyhedra. The second substructure, V₁₂Sn, is built from Q-polyhedra and 20-vertex pseudo-Frank-Kasper polyhedra and reveals similarities with the Be₁₂Ti type. The list of known structures with Frank-Kasper polyhedra was updated and new features governing this family of compounds were discovered. It was found that, among the number of possible hypothetical structures, only one combination derived from the Yarmolyuk-Kripyakevich criterion, is observed for a particular number of icosahedra.

The four Frank-Kasper polyhedra

Keywords

Intermetallics / Tetrahedrally close-packed structure / Frank-Kasper polyhedra / Yarmolyuk-Kripyakevich criterion