Stability and properties of six new Ru3Al structures: A first-principles study of mechanical, electronic, and superconducting properties

Abstract

Ruthenium–aluminium (Ru–Al) alloys demonstrate excellent properties; however, the Ru3Al structure has a higher formation energy than those of other Ru–Al structures. Herein, to identify more stable Ru3Al structures, we employed the CALYPSO code and discovered six stable structures: one hexagonal structure, two monoclinic structures and three orthorhombic structures. First-principles calculations and the density functional theory were used to assess their mechanical, electrical and superconducting properties. The formation energies of these newly discovered Ru3Al structures were lower than those of previously proposed structures, confirming their thermodynamic stability. Elastic constant calculations indicated that all the structures were mechanically stable and ductile. Moreover, electronic structure analyses revealed that the structures were metallic, primarily owing to the contribution of Ru d orbitals. Phonon dispersion and density of states analyses also confirmed the dynamic stability of the structures, with low-frequency phonons contributing considerably to electron–phonon coupling. The superconducting transition temperatures (Tc) of the structures were calculated using the Allen–Dynes-modified McMillan equation. The Cmcm structure showed the highest Tc of 3.99 K, and the P2/c structure showed the lowest Tc of 1.56 K. Overall, this study identified six novel and stable Ru3Al structures with good mechanical and superconducting properties, potentially advancing the development of Ru–Al-based superconductors.