Superconductivity in CeBeH 8 and CeBH 8 at moderate pressures.

High-pressure structural searches of superhydrides CeBeH 8 and CeBH 8 were performed under ambient pressure up to 300 GPa. We identifyFm3‾m-CeBeH 8 with a superconducting transition temperature T c of 56 K at 10 GPa. Two more phases with spacegroupR3‾mandC2/m, were investigated within the increasing pressures. CeBH 8 shows a similar phase transition process as CeBeH 8 but with higher transition pressures and higher T c .Fm3‾m-CeBH 8 is predicted to be superconducting above 120 GPa with a maximum T c of 118 K at 150 GPa.R3‾m-CeBH 8 andC2/m-CeBH 8 are dynamically stable above 120 GPa and 100 GPa, respectively. The maximum T c is 123 K at 195 GPa forR3‾m-CeBH 8 , and 115 K at 350 GPa forC2/m-CeBH 8 . Our work enriches the family of ternary hydrides and may provide a useful guideline for further search for superconducting hydrides at low and moderate pressures.