Hydrogen stoichiometry in the cubic Pm-3m MgIrHx impurity phase

Determine the hydrogen stoichiometry x in the cubic Pm-3m impurity phase assigned as MgIrH_x that is observed as a minority phase in autoclave-synthesized Mg–Ir hydride precursors, specifically establishing whether the phase is a true hydride (e.g., MgIrH_3) or an alloy with x = 0, consistent with density functional theory volume predictions.

Background

In the autoclave-synthesized precursor material, a minor cubic phase with Pm-3m symmetry was observed. The authors assign it as MgIrH_x based on volume considerations from DFT that span compositions from MgIr to MgIrH_3.

However, the exact hydrogen content remains undetermined, and resolving x is necessary to clarify whether this phase is an alloy (x = 0) or a hydride, which impacts interpretation of impurity effects and equation-of-state analysis.

References

Here, we assign the composition as MgIrH$_x$, where $x$ is unknown and possibly zero, based on DFT volume predictions that range between MgIr and MgIrH$_3$.

— Synthesis of Mg$_2$IrH$_5$: A potential pathway to high-$T_c$ hydride superconductivity at ambient pressure (2406.09538 - Hansen et al., 13 Jun 2024) in Supplemental Material, subsection "Compressibility of Pm-3m phase"