Synthesis of Mg2IrH5 : A potential pathway to high- Tc hydride superconductivity at ambient pressure

Following long-standing predictions associated with hydrogen, high-temperature superconductivity has recently been observed in several hydride-based materials. Nevertheless, these high-${T}_{c}$ phases only exist at extremely high pressures, and achieving high transition temperatures at ambient pressure remains a major challenge. Recent predictions of the complex hydride ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ may help overcome this challenge with calculations of high-${T}_{c}$ superconductivity ($65\phantom{\rule{0.28em}{0ex}}\mathrm{K}<{T}_{c}<170\phantom{\rule{4.pt}{0ex}}\text{K}$) in a material that is stable at atmospheric pressure. In this paper, the synthesis of ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ was targeted over a broad range of $P\text{\ensuremath{-}}T$ conditions, and the resulting products were characterized using x-ray diffraction (XRD) and vibrational spectroscopy, in concert with first-principles calculations. The results indicate that the charge-balanced complex hydride ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{5}$ is more stable over all conditions tested up to approximately 28 GPa. The resulting hydride is isostructural with the predicted superconducting ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ phase except for a single hydrogen vacancy, which shows a favorable replacement barrier upon insertion of hydrogen into the lattice. Bulk ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{5}$ is readily accessible at mild $P\text{\ensuremath{-}}T$ conditions and may thus represent a convenient platform to access superconducting ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ via nonequilibrium processing methods. Finally, the critical factors influencing the calculated range of superconducting transition temperatures for this material are discussed.