Face-Centered Cubic Refractory Alloys Prepared from Single-Source Precursors

Three binary fcc-structured alloys (fcc-Ir_0.50Pt_0.50, fcc-Rh_0.66Pt_0.33 and fcc-Rh_0.50Pd_0.50) were prepared from [Ir(NH₃)₅Cl][PtCl₆], [Ir(NH₃)₅Cl][PtBr₆], [Rh(NH₃)₅Cl]₂[PtCl₆]Cl₂ and [Rh(NH₃)₅Cl][PdCl₄]·H₂O, respectively, as single-source precursors. All alloys were prepared by thermal decomposition in gaseous hydrogen flow below 800 °C. Fcc-Ir_0.50Pt_0.50 and fcc-Rh_0.50Pd_0.50 correspond to miscibility gaps on binary metallic phase diagrams and can be considered as metastable alloys. Detailed comparison of [Ir(NH₃)₅Cl][PtCl₆] and [Ir(NH₃)₅Cl][PtBr₆] crystal structures suggests that two isoformular salts are not isostructural. In [Ir(NH₃)₅Cl][PtBr₆], specific Br…Br interactions are responsible for a crystal structure arrangement. Room temperature compressibility of fcc-Ir_0.50Pt_0.50, fcc-Rh_0.66Pt_0.33 and fcc-Rh_0.50Pd_0.50 has been investigated up to 50 GPa in diamond anvil cells. All investigated fcc-structured binary alloys are stable under compression. Atomic volumes and bulk moduli show good agreement with ideal solutions model. For fcc-Ir_0.50Pt_0.50, V₀/Z = 14.597(6) ų·atom^-1, B₀ = 321(6) GPa and B₀' = 6(1); for fcc-Rh_0.66Pt_0.33, V₀/Z = 14.211(3) ų·atom^-1, B₀ =259(1) GPa and B₀' = 6.66(9) and for fcc-Rh_0.50Pd_0.50, V₀/Z = 14.18(2) ų·atom^-1, B₀ =223(4) GPa and B₀' = 5.0(3).