Structure and superconductivity of protactinium hydrides under high pressure

We systematically study the stability, crystal structure, electronic property, and superconductivity of protactinium hydride (PaH _n ) (n  =  1-9) at a pressure range of 1 atm to 300 GPa by using the first principle of density functional theory. PaH _n compounds are very rich, featuring six stoichiometries, such as PaH, PaH₃, PaH₄, PaH₅, PaH₈ and PaH₉. PaH₈ possesses the highly symmetrical crystal structure Fm-3m with cubic H8 units, which is predicted to be thermodynamically stable above 32 GPa. This phase maintains a dynamically stable decompression at 10 GPa. Electron-phonon coupling (EPC) calculations show that Fm-3m-PaH₈ exhibits high superconducting critical transition temperature (T _c) value of 79 K at 10 GPa due to a strong EPC and large logarithmic average frequency. The T _c values of Fm-3m-PaH₈ decrease with increasing pressure. Interestingly, superconducting PaH₈ appears at low pressure, prompting experimental research.