Thorium-doped boron-carbon clathrates: Superconductivity and tunable electronic properties under pressure

This study explores the potential of thorium-doped boron-carbon clathrates to possess beneficial superconducting and mechanical properties as a function of pressure. Using first-principles density functional theory calculations, we assess the dynamic stability, electronic structure, and superconductivity of ThB₃C₃ and ThB₄C₂, considering the electron-doped superconducting nature of ThB₃C₃ and the unexpected metallic behavior of ThB₄C₂, despite it being isoelectronic with diamond. ThB₃C₃ adopts a cubic Pm3̄n structure, dynamically stable between 70 and 200 GPa, while ThB₄C₂ adopts a tetragonal I4/mmm structure, remaining dynamically stable from ambient pressure up to 200 GPa. Convex-hull analysis reveals their thermodynamic stability under high pressure: ThB₄C₂ is stable at both 100 and 200 GPa, whereas ThB₃C₃ remains metastable across the pressure range considered. Our work is the first to demonstrate that this family of compounds can be metalized via electron doping, as opposed to the hole doping that has been studied to date. ThB₃C₃ is predicted to exhibit a superconducting transition temperature (T_c) of 56 K at 70 GPa, driven by strong electron-phonon coupling (EPC), while ThB₄C₂, despite its lower T_c of 0.7 K, is found to maintain superconductivity at ambient pressure. These results emphasize the potential of thorium-doped boron-carbon clathrates as promising candidate materials with tunable superconducting, electronic, and mechanical properties, paving the way for future experimental synthesis and practical applications.