Iridium shows remarkable stability at extreme conditions

Iridium belongs to the 5-d transition metals which show the highest melting points among other elements (for Iridium it 2719 K at ambient pressure). Iridium also exhibitsexceptional resistance to corrosion and deformation, which makes it invaluable in technologies that must withstand the most demanding environments—from turbine blades and nuclear reactors to space probes operating near the Sun. However, despite decades of study, its pressure–temperature phase diagram had remained largely unexplored beyond moderate conditions.

Angelika Rosa, scientist at the ESRF and co-author of the publication, explains: “Exploring the phase diagram and thermo-elastic parameters of an incompressible and thermally stable material like iridium presents significant challenges. This is mainly due to the need for high-precision pressure and temperature measurements, as well as the requirement to reach extreme conditions to induce detectable changes.”

Now a team led by the Universitat de Valencia (Spain), in collaboration with the ESRF and Diamond Light source, has carried out X-ray diffraction experiments using diamond anvil cells to map the behaviour of iridium at pressures up to 101 GPa and temperatures above 5600 K, which are conditions similar to those found deep inside planetary interiors.

In particular, the team employed resistively heated (RH-DAC) and laser-heated diamond anvil cells (LH-DAC), coupled with advanced X-ray diffraction (XRD) techniques.

The results showed that iridium’s face-centered cubic (fcc) structure remains remarkably stable under all tested conditions. They also provide new melting data and a precise thermal equation of state that will help refine current models of planetary interiors formation based on geochemical data and improve the design of materials for extreme environments.

The scientists also compared iridium with related transition metals, including platinum, rhodium and ruthenium. This revealed a systematic link between elasticity and thermal expansion—offering a simple framework to describe how these elements behave under extreme conditions.

Until now, only a single experimental melting point for iridium had ever been measured. The new results close that gap and offer new experimental benchmarks for theoretical models and insights into the properties of refractory metals under conditions relevant to planetary science and high-pressure physics.

Reference:

Anzellini, S., et al. Commun Mater 6, 221 (2025). https://doi.org/10.1038/s43246-025-00963-4

Text by Montserrat Capellas Espuny

Top image: Image plates showing the textural evolution observed at around 26 GPa for Ir and KCl as a function of T. Specifically, at a 1930 K, b 2887 K, c 3250 K and d 3477 K.