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

Abstract

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$^1 {−1}$, B$_0$ = 341(10) GPa, and B0' = 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