Giant enhancement of superconducting critical temperature in substitutional alloy (La,Ce)H 9 .

A sharp focus of current research on superconducting superhydrides is to raise their critical temperature T _c at moderate pressures. Here, we report a discovery of giant enhancement of T _c in CeH ₉ obtained via random substitution of half Ce by La, leading to equal-atomic (La,Ce)H ₉ alloy stabilized by maximum configurational entropy, containing the LaH ₉ unit that is unstable in pure compound form. The synthesized (La,Ce)H ₉ alloy exhibits T _c of 148-178 K in the pressure range of 97-172 GPa, representing up to 80% enhancement of T _c compared to pure CeH ₉ and showcasing the highest T _c at sub-megabar pressure among the known superhydrides. This work demonstrates substitutional alloying as a highly effective enabling tool for substantially enhancing T _c via atypical compositional modulation inside suitably selected host crystal. This optimal substitutional alloying approach opens a promising avenue for synthesis of high-entropy multinary superhydrides that may exhibit further increased T _c at even lower pressures.
(© 2022. The Author(s).)