Competing Electronic and Size Effects When Substituting 3d Elements for Nb in Nb3Ru5B2 En Route to the Quaternary Phases (Nb2–xScx)4gNb2aRu5B2 (1 ≤ x < 2), Nb3–xMxRu5B2 (M = Ti, V; x ≈ 1), and Nb2+xM1–xRu5B2 (M = Cr, Mn, Fe, Co, Ni; 0 < x ≤ 0.5)

Abstract

AbstractSingle crystals and polycrystalline samples of (Nb2–xScx)4gNb2aRu5B2 (1 ≤ x < 2), Nb3–xMxRu5B2 (M = Ti, V; x ≈ 1), and Nb2+xM1–xRu5B2 (M = Cr, Mn, Fe, Co, Ni; 0 < x ≤ 0.5) were synthesized from the elements and characterized by single‐crystal and powder X‐ray diffraction as well as energy‐dispersive X‐ray analysis. These phases are substitutional variants of the recently reported Nb3Ru5B2 phase and crystallize in the Ti3Co5B2‐type structure (tetragonal, space group P4/mbm, no. 127). The structure consists of layers of ruthenium atoms that build trigonal, tetragonal, and pentagonal prisms, in which the other atoms are incorporated. The larger 3d metals, Sc, Ti, and V are found on the larger pentagonal prisms, together with niobium, and also (except for Sc) on the tetragonal prisms. The smaller 3d metals, Cr–Ni, are only found on the tetragonal prisms, but also mix with niobium. DFT calculations on the ternary phase Nb3Ru5B2 suggested that the reason for this site mixing can be found in its electronic structure and the application of the rigid band model proposed a valence electron (VE) range between ca. 58 and 64 for the derived stable phases. All synthesized quaternary phases fit very well within this VE range.