First-principles investigation of the phase diagram and superconducting properties of the Sc–Mg–H system under high pressure

Abstract

Superconductors, known for their zero electrical resistance and perfect diamagnetism, hold great promise for broad applications. In this study, we employed particle swarm optimization combined with first-principles calculations to predict the structures of Sc–Mg–H compounds under elevated pressure. Our approach identified four stable configurations within the pressure range of 30 to 250 GPa: ScMgH₈-P4/mmm (stable from 30 to 250 GPa), ScMgH₁₂-Cmmm (stable from 80 to 250 GPa), Sc₂MgH₁₈-Pm1 (stable from 110 to 250 GPa), and ScMg₂H₁₈-Pm1 (stable from 200 to 250 GPa). Through enthalpy calculations, we constructed the pressure-composition phase diagram of the Sc–Mg–H system and explored the stability and superconductivity of these compounds. The superconducting transition temperature (T_c) of Sc₂MgH₁₈ reaches 112 K at 150 GPa, ScMgH₈ (at 80 GPa) and ScMgH₁₂ (at 100 GPa) have T_c values of 56 K and 87 K, respectively. As the hydrogen content increases, ScMg₂H₁₈ requires the highest stabilizing pressure of 200 GPa and has a T_c of 98 K. These findings offer valuable insights for future high-temperature superconductor research and provide theoretical guidance for synthesizing novel materials with superior properties.