As compressed hydrides constantly refresh the records of superconducting critical temperatures (T_c) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P6₃/mmc-LaH₁₀) stabilized at 146 GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with T_c ~ 178 K, and this value is enhanced to a maximum T_c ~ 223 K at 164 GPa. A huge upper critical magnetic field value H_c2(0) reaches 223 T at 146 GPa. The small volume expansion of P6₃/mmc-(La, Al) H₁₀ compared with the binary LaH₁₀ indicates the possible interstitial sites of Al atoms filling into the La-H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system.

 

hydrides,superconductivity,metastable,high pressure