Ternary ScC₂H₈ Superconductor at Moderate Pressure

The pursuit of high-temperature superconducting superhydrides has entered a novel stage, departing from examining binary hydrides and shifting the attention toward ternary compounds characterized by potentially better superconducting properties. Theoretical and experimental endeavors have unveiled auspicious ternary hydrogen-rich materials capable of exhibiting superconductivity at temperatures close to room temperature and high pressure. Nonetheless, synthesizing ternary compounds with a well-defined crystal structure suitable for sustaining high-temperature superconductivity under low pressures remains a formidable challenge. Herein, we perform a comprehensive theoretical analysis of the ScH10 and ScX2H8 compounds, where X denotes the small-radius elements (B, C, N, Al, Si, and P). Our calculations indicate that only ternary Fm3̅m-ScC2H8 hydride is simultaneously energetically, dynamically, and thermally stable above 50 GPa and exhibits metallic properties and superconducting features with a maximal critical temperature up to 57 K at 200 GPa. Moreover, our findings prove the strong-coupling electron–phonon pairing mechanism in ScC2H8 and greatly expand the space for exploring high-temperature and low-pressure superhydrides.