Researchers map hidden crystal structures of iridium under extreme pressure
Scientists used computer modeling to predict how iridium—a precious metal used in catalysts, electronics, and aerospace—transforms under crushing pressure. The findings reveal unexpected crystal arrangements that could help manufacturers better predict material behavior in high-stress applications and refine how we extract and process this valuable element.
Originaltitel: Ab initio phase diagram of iridium
<p>The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to less than or similar to 65 GPa) is found for the equation of state (EOS) of Ir, it is the third-order Birch-Murnaghan EOS with B-0 = 5 rather than the more widely accepted B-0 = 4 that describes our ab initio data to higher pressure (P). Our results suggest the existence of a random-stacking hexagonal close-packed structure of iridium at high P. We offer an explanation for the 14-layer hexagonal structure observed in experiments by Cerenius and Dubrovinsky.</p>