Equations of state of rhodium, iridium and their alloys up to 70 GPa

Knowledge of the compressional and thermal behaviour of metals and alloys is of a high fundamental and applied value. In this work, we studied the behaviour of Ir, Rh, and their fcc-structured alloys, Ir _0.42 Rh _0.58 and Ir _0.26 Os _0.05 Pt _0.31 Rh _0.23 Ru _0.15 , up to 70 GPa using the diamond anvil cell technique with synchrotron X-ray diffraction. We found that all these materials are structurally stable upon room-temperature hydrostatic compression in the whole pressure interval, as well as upon heating to 2273 K both at ambient and high pressure. Rh, Ir _0.42 Rh _0.58 and Ir _0.26 Os _0.05 Pt _0.31 Rh _0.23 Ru _0.15 were investigated under static compression for the first time. According to our data, the compressibility of Ir, Rh, fcc–Ir _0.42 Rh _0.58 , and fcc–Ir _0.26 Os _0.05 Pt _0.31 Rh _0.23 Ru _0.15 , can be described with the 3rd order Birch-Murnaghan equation of state with the following parameters: V ₀ = 14.14(6) Å ³ ·atom ⁻¹ , B ₀ = 341(10) GPa, and B ₀ ' = 4.7(3); V ₀ = 13.73(7) Å ³ ·atom ⁻¹ , B ₀ = 301(9) GPa, and B ₀ ' = 3.1(2); V ₀ = 13.90(8) Å ³ ·atom ⁻¹ , B ₀ = 317(17) GPa, and B ₀ ' = 6.0(5); V ₀ = 14.16(9) Å ³ ·atom ⁻¹ , B ₀ = 300(22) GPa, B ₀ ' = 6(1), where V ₀ is the unit cell volume, B ₀ and B ₀ ' – are the bulk modulus and its pressure derivative.