First-Principles Investigation of the Phase Diagram and Superconducting Properties of the Sc-Mg-H System under High Pressure

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-P3̄m1 (stable from 110 to 250 GPa), and ScMg2H18-P3̄m1 (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 (Tc) of Sc2MgH18 reaches 112 K at 150 GPa, ScMgH8 (at 80 GPa) and ScMgH12 (at 100 GPa) have Tc 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 Tc 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.