High-pressure stabilization of Mg2IrH7: Structural proximity to a high-Tc superconducting phase

Mg IrH is a metastable complex metal hydride with a predicted superconducting transition tem- perature as high as 170K at ambient pressure. Following the synthesis of isomorphic, insulating Mg IrH at low pressure, higher-pressure studies were conducted to investigate the phase behavior and compound formation in this system. X-ray diffraction and Raman spectroscopic measure- ments, combined with ab initio calculations, support the formation of cubic Mg2IrH7 above ca. 40 GPa. This phase may coexist with a related hexagonal hydride with an estimated composition near Mg IrH . Electrical transport measurements suggest that cubic Mg IrH is insulating, in agreement with ab initio predictions, and persists during room-temperature decompression until ∼20GPa before reverting back to cubic Mg2IrH5. The experimental results support ground-state structure predictions in the Mg–Ir–H system, and the formation of two nearly identical phases with surrounding compositions may open new opportunities to access superconducting Mg IrH through non-equilibrium processing pathways.