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 (65 K~<~Tc~<~ 170 K) in a material that is stable at atmospheric pressure. In this work, 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 ca 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 non-equilibrium processing methods.