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-Tc 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 Mg2IrH6 may help overcome this challenge with calculations of high-Tc superconductivity (65K<Tc<170K) in a material that is stable at atmospheric pressure. In this paper, the synthesis of Mg2IrH6 was targeted over a broad range of P-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 Mg2IrH5 is more stable over all conditions tested up to approximately 28 GPa. The resulting hydride is isostructural with the predicted superconducting Mg2IrH6 phase except for a single hydrogen vacancy, which shows a favorable replacement barrier upon insertion of hydrogen into the lattice. Bulk Mg2IrH5 is readily accessible at mild P-T conditions and may thus represent a convenient platform to access superconducting Mg2IrH6 via nonequilibrium processing methods. Finally, the critical factors influencing the calculated range of superconducting transition temperatures for this material are discussed.