In situ characterization of the phase diagram of Ir via X-ray diffraction coupled with resistive and laser-heated diamond anvil cell

Abstract Transition metals, including Iridium, are crucial for understanding planetary cores and developing critical technologies due to their unique properties under extreme high-pressure and high-temperature conditions. Although Ir’s room-temperature phase remains stable, its pressure-temperature phase diagram is largely unknown, with only a single experimental melting point reported previously. A notable gap in knowledge is the lack of experimental evidence for solid-solid phase transitions predicted by theoretical models. Here we show a new investigation into the phase diagram of iridium, employing a combination of resistive-heated and laser-heated diamond anvil cells coupled with synchrotron X-ray diffraction. Our findings confirm that Ir maintains its face-centered cubic structure up to 101 GPa and 5600 K. We determined five new melting points that corroborate computational predictions, providing a more robust foundation for the melting curve. The resulting thermal equation of state offers a definitive dataset that can serve as a reliable pressure standard and advance the design of technologies using Ir.