Superconductivity of ternary XBeH₈ hydrides (X = La, Ba, Pr, and Ac) under high pressure

Although extensive studies have been conducted on binary hydrides, an ideal superconductor at ambient temperature and pressure has yet to be discovered. Ternary hydrides increase the possibility of different crystal structures exponentially and can make up for the poor stability and the disadvantage of low T_c caused by the single doping element (X) in binary hydrides (XH_n). In this work, we systematically studied the structural stability, bonding properties, electronic structure, electron-phonon coupling and superconducting properties of the XBeH₈ (X = La, Ac, Ba, and Pr) system within the pressure range of 0-500 GPa. First, phonon spectra were used to determine the stability regimes influenced by different X elements. Second, we analyzed the atomic interactions based on the electronic structure. We further calculated the electron-phonon coupling and superconducting properties of the stable structures. The T_c of AcBeH₈ (LaBeH₈) was calculated to reach 142 K at 50 GPa (137 K at 20 GPa). Furthermore, the Fm3̄m phase of PrBeH₈ has been reported for the first time. It exhibits a large λ of 3.27 at 30 GPa, with a predicted T_c of 148 K. Additionally, PrBeH₈ has been predicted to reach a T_c of 215 K under 400 GPa.