Dopant and defect engineering of FeCoVNi high-entropy alloy: A DFT perspective

The effects of substitutional doping with selenium as well as vacancy defects on the physical properties of FeCoVNi high-entropy alloy are comprehensively investigated using density functional theory. The pristine alloy favors the face-centered cubic crystal structure due to its high valence electron concentration, and selenium incorporation or vacancies only introduce slight lattice contraction. At low selenium concentrations (FeCoVNi 0.875 Se 0.125 and FeCoVNi 0.75 Se 0.25 ) doped structures are dynamically unstable, while at higher doping levels (FeCoVNi 0.625 Se 0.375 and FeCoVNi 0.5 Se 0.5 ) in addition to being dynamically stable, the doped structures have significantly enhanced mechanical strength, reduced elastic anisotropy, and they preserve good ductility. Thermal analysis reveals that selenium strongly modifies phonon behavior, with the alloy FeCoVNi 0.625 Se 0.375 exhibiting the highest sound velocity and Debye temperature, indicating superior lattice stiffness and thermal stability. On the other hand vacancy defects increase lattice anharmonicity and phonon scattering. Considered structures remain metallic after doping and introduction of vacancies, but with markedly reduced magnetic moments. These results pave the way for tailoring the performance of FeCoVNi-based high entropy alloys for applications that require both flexibility and robust magnetic performance such as advanced sensors and actuators.