Pm 3 n (La, Ce) 4 H 23 Phase: A Low-Pressure Hydride Superconductor near Liquid-Nitrogen Temperature

Hydrides are widely regarded as promising candidates for near room-temperature superconductivity. A holy grail in this field is to find high-temperature superconducting hydrides at moderate pressure or even ambient conditions. Although numerous theoretical predictions suggest that high-temperature hydride superconductors at ambient conditions are within reach, the primary task is to find experimental methods to decrease the necessary synthesis pressure of hydride superconductors and recover them to lower pressure. By selecting precursor systems with similar metal frameworks rather than closely matched hydride structures, we successfully synthesize a Pm 3̅ n phase (La, Ce) 4 H 23 . The compound exhibits a superconducting critical temperature of 78 K at 89 GPa, while its minimum synthesis pressure (67 GPa) is reduced by ∼29% compared with the binary La 4 H 23 . These results show that targeting a relevant metal lattice and using a solid-solution alloy offer an experimentally practical strategy for realizing high superconducting critical temperature at progressively lower pressures.