Actinium Hydrides AcH10, AcH12, and AcH16 as High-Temperature Conventional Superconductors.

The stability of numerous unexpected actinium hydrides was predicted via the evolutionary algorithm USPEX. The electron-phonon interaction was investigated for the hydrogen-richest and most symmetric phases: R3̅ m-AcH10, I4/ mmm-AcH12, and P6̅ m2-AcH16. Predicted structures of actinium hydrides are consistent with all previously studied Ac-H phases and demonstrate phonon-mediated high-temperature superconductivity with TC in the range of 204-251 K for R3̅ m-AcH10 at 200 GPa and 199-241 K for P6̅ m2-AcH16 at 150 GPa, which was estimated by directly solving the Eliashberg equation. Actinium belongs to the series of d1 elements (Sc-Y-La-Ac) that form high- TC superconducting (HTSC) hydrides. Combining this observation with previous predictions of p0-HTSC hydrides (MgH6 and CaH6), we propose that p0 and d1 metals with low-lying empty orbitals tend to form phonon-mediated HTSC metal polyhydrides.