First principles study of structural, electronic and mechanical properties of ternary Ru-Cr-X alloys

Abstract

We have investigated the effect of doping on the structural, electronic and mechanical properties of A15 RuCr3 and A15 Ru3Cr alloys using density functional theory. Various transition metal dopants, namely V, Mn, Fe, Co, Zr, Mo, Pd, Pt and Re were introduced in the 2x2x2 supercells constructed from the optimized unit cells of RuCr3 and Ru3Cr binary alloys. The calculated lattice constants for the pure metals, doped and undoped Ru48Cr16 and Cr48Ru16 alloys were determined using the generalized gradient approximation. The results are in overall good agreement with the experimental and previous theoretical data. The relaxed lattice constants for the X doped Ru48Cr16 and Cr48Ru16 structures (X = V, Mn, Fe, Co, Zr, Mo, Pd, Pt and Re) remained the same as the unrelaxed structures because the supercells were produced from the optimized unit cells. All the studied undoped systems were predicted to be unstable, in agreement with the previous theoretical study. Stability of doped Ru48Cr16 and Cr48Ru16 compounds were investigated based on the heats of formation. In general, the Mn, Fe and Mo-doped compositions exhibited negative heats of formation whereas all the remaining dopants displayed positive heats of formation. The addition of Mn, Fe and Mo dopants to the unstable Ru48Cr16 and Cr48Ru16 tuned the heats of formation and enhanced the stability of the systems. The magnetic properties of the pure metals and their ternaries were studied, the metallic Mn was found to have a high-optimized magnetic moment of 5.0 μB while the optimized magnetic moment for Zr was found to be -0.00059 μB. Mn and Zr influence Ru-Cr systems to obtain high magnetization and low magnetization respectively. Densities of states were investigated to analyze the nature and stability of the alloys. It was found that all the Mn, Fe and Mo-doped Cr48Ru16 and Ru48Cr16 systems show full-metallic behavior. Furthermore, the X-doped Cr48Ru16 compounds (X = Mn, Fe and Mo) were found to be more stable than the X-doped Ru48Cr16 compounds. The observed results are due to Cr rich alloys having low density of states around Fermi energy than Ru rich alloys. This finding is consistent with the heats of formation results. Elastic properties were studied to determine the strength and further analyze the stability of the systems. The ratio of bulk to shear modulus, and Poisson’s ratio are greater than 1.75 and 0.3 respectively indicating that the studied X-doped systems are ductile. In addition, the elastic constants revealed that the systems are mechanically stable. The Mn, Fe and Mo-doped Ru48Cr16 and Cr48Ru16 could be considered as corrosion resistant materials in high temperature applications