A general approach to qualitatively and graphically characterize the diffuse behavior of interstitial nonmetallic atoms in multi-principal element alloys based on site preference

It is urgent to establish a series of reasonable and general approaches to qualitatively and graphically characterize the four core effects of multi-principal element alloys (MPEAs) based on the inherent site preference. In this contribution, a qualitatively and graphically characterizing approach to the diffusion behavior of interstitial nonmetallic atoms diffusing along the neighboring octahedra in MPEAs was explored intensively. For this purpose, the C atom diffusing along the neighboring octahedra in FCC_CoNiV MPEA with (V_1.0000)_1a(Co_0.4445Ni_0.4444V_0.1111)_3c, a constant ordered occupying configuration predicted in our previous paper, was demonstrated in detail. Six distinct diffusion paths along [110], [101], and [011] directions on XY, XZ, and YZ planes of FCC_CoNiV MPEA with forward and backward diffusion directions were explored one by one, respectively. The diffusion energy barrier, diffusion coefficient, diffusion constant, and activation energy were derived by employing first-principles calculations based on density functional theory alongside the Climbing Image Nudged Elastic Band method. Unlike diffusing behavior in pure metallic elements, the non-periodic diffusion energy barrier waves are revealed for the real FCC_CoNiV MPEA structure. The significant variations in the diffusion energy barriers are influenced by the atomic environment, particularly the interaction between V and C atoms, which enhances the localization of electrons and increases the overall diffusion energy barrier. The energy barriers show similar trends along six paths, but significant variations occur across different octahedral sites.