On the other hand, Ir is used for the construction of thermocouples and encapsulators of nuclear-powered electrical generators in space technology 2. These properties make Ir useful for many technological applications for instance, as a high-pressure gasket or as a pressure calibrant in high temperature and high-pressure (HP) diamond-anvil cell (DAC) experiments. On top of that, Ir has an extremely high thermal stability, being able to preserve mechanical stability at temperatures above 2000 ☌ and it is not easily susceptible to corrosion. It is the second densest elemental metal having an ambient pressure density of 22.65 g/cc at T = 0 K and 22.56 g/cc at T = 293.15 K, and a shear modulus, G o = 210 GPa, comparable to that of osmium, G o = 220 GPa, at ambient conditions 1. Iridium (Ir), with electronic structure 4d 105s 25p 64f 145d 76s 2, is one of the most incompressible 5d transition metals with face-centered cubic (fcc) structure.
The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions. X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1).
Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties.