Lower-pressure synthesis of high-Tc LaSc2H24

Determine whether the hexagonal P6/mmm LaSc2H24 superhydride that exhibits room-temperature superconductivity can be synthesized at pressures below approximately 250–260 GPa while retaining a high superconducting critical temperature.

Background

Initial synthesis attempts carried out below 200 GPa produced superconducting transitions around 250 K, attributed to LaH10 or an unidentified La–Sc–H phase, indicating that the targeted LaSc2H24 had likely not formed under those conditions.

Further attempts between 200 and 250 GPa also did not yield higher critical temperatures, whereas increasing the synthesis pressure to ~260 GPa produced a pronounced enhancement of superconductivity and XRD patterns consistent with the predicted P6/mmm LaSc2H24 structure.

Although theory suggests LaSc2H24 is thermodynamically stable at pressures as low as 167 GPa, the experiments so far indicate improved formation at higher pressures, motivating the explicit question of whether this high-Tc phase can be synthesized at lower pressures.