Novel compounds in the Sc-rich part of the systems Sc-{Co,Pd,Pt}-Ga: Structure and bonding

Author(s): V.V. Romaka, Gerda Rogl, J. Buršík, A. Grytsiv, G. Giester, P. Rogl
Abstract: The present paper comprises a detailed structural analysis of two novel compounds in the Sc-Co-Ga system: τ₃-Sc₅₀Co₁₃Ga₃ (space group Fm-3; ε-Mg_26-xAg_7+x type), and τ₄-Sc₆Co_1.73+x+yGa_1-x (space group Immm; x=0.43; y=0.14; Ho₆Co₂Ga derivative type). Although alloys in the isothermal section are oxygen-free, the alloy of τ_3, prepared for single crystal growth via partial melting in an alumina crucible, contained a minor amount of oxygen and can be considered as oxygen-stabilized Sc₅₀Co₁₃Ga₃O_1.1 (WDX-data). A search for homologous compounds in the systems Sc-{Pd,Pt}-Ga prompted the existence of two compounds Sc₅₄{Pd,Pt,Ga}₁₇, which from X-ray single crystal analyses proved both to be isotypic with the Hf₅₄Os₁₇-type structure (space group Immm). Whereas Sc₅₄(Pd_0.652Ga_0.348)₁₇ has a very limited homogeneity region at 850°C, Sc₅₄(Pt_1-xGa_x)₁₇ exhibits at 850°C a large homogeneity region (0<x<0.28) extending from Ga-rich Sc₇₆Pt_17.2Ga_6.8≡Sc₅₄(Pt_0.72Ga_0.28)₁₇ to novel binary Sc₅₄Pt₁₇. Interestingly, against the usual trend of solution hardening, hardness, Young's modulus and fracture toughness all decrease with increasing Ga-content: this effect is less pronounced for Sc₅₄(Pd_1-xGa_x)₁₇ than for Sc₅₄(Pt_1-xGa_x)₁₇ and is in line with DFT calculations indicating a weakening of bonding with increasing Ga content, thereby overcompensating the solution hardening effect. DFT modeling showed a common bonding feature for all the studied compounds – a strong electron localization inside the Sc₆ octahedra, stacking of which leads to the formation of Mackay icosahedra in Sc₅₄(Pd_1-xGa_x)₁₇, Sc₅₄(Pt_1-xGa_x)₁₇, and Sc₅₀Co₁₃Ga₃. The band structure of Sc₆Co_2.25Ga_0.625 and Sc₅₀Co₁₃Ga₃ indicates their metallic behavior, while Sc₅₄(Pd_1-xGa_x)₁₇ and Sc₅₄(Pt_1-xGa_x)₁₇ show distinct semimetal features. All investigated compounds in this work show similar trends in Bader charge distribution with a positively charged Sc-sublattice and a negatively charged sublattice formed by transition metals (Co, Pd, Pt) and Ga.
Organisation(s): Department of Materials Chemistry, Department of Mineralogy and Crystallography
External organisation(s): Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, Czech Academy of Sciences
Journal: Journal of Alloys and Compounds
Volume: 998
Pages: 1-18
No. of pages: 18
ISSN: 0925-8388
DOI: https://doi.org/10.1016/j.jallcom.2024.174864
Publication date: 09-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 105116 Mineralogy, 105113 Crystallography, 104017 Physical chemistry
Keywords
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Portal url: https://ucrisportal.univie.ac.at/en/publications/e971ad67-0c23-4f39-a81a-fa9f1f228b69

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