Distinct point defect behaviours in body-centered cubic medium-entropy alloy NbZrTi induced by severe lattice distortion

The point defect properties of body-centered cubic medium-entropy alloy NbZrTi were studied by firstprinciples calculations.Due to severe lattice distortion, a significant portion of conventional vacancy and interstitial structures are unstable and require large structural relaxation, indicating an irregular energy landscape with large site-to-site variations.The average vacancy and interstitial formation energy are 0.95 eV ± 0.34 eV and 1.92 eV ± 0.39 eV, respectively, much lower than that of Nb (2.77 eV and 4.38 eV).The vacancy migration energy exhibits a wide distribution extending to 0 eV, resulting in preferential vacancy migration through low barrier sites.The interstitial diffusion is slower than that of pure Nb due to the reduction of long < 111 > diffusion induced by the site-to-site variations in stable interstitial orientations.Ti atoms diffuse much faster than Nb and Zr atoms due to the preferential interstitial binding with Ti.The effect of atomic composition and short-range order on elemental and total interstitial diffusion was also investigated.The obtained first-principles results are important for the development of interatomic potentials for radiation damage studies.When irradiated with 3-MeV Fe ions at 675 • C to a peak dose of ∼100 dpa, NbZrTi reduced the void formation at high temperature compared to Nb owing to its higher equilibrium vacancy concentration and closer mobility between vacancies and interstitial atoms.