Local Coordination and Short‐Range Order Govern Initial Oxygen Incorporation in High‐Entropy Carbonitrides

Abstract

High‐entropy carbonitrides (HECNs) are promising high‐temperature functional materials whose oxidation resistance and mechanisms attract extensive attention. Subjected to prolonged high temperature and oxygen, HECNs undergo slow oxidation. Cumbersome experiments and limitations of macroscopic analysis hinder the optimization of oxidation‐resistant compositions. Combining density functional theory (DFT), a local potential model (LPM), and Monte Carlo simulations (MC), this work investigates the initial oxidation of rock‐salt (MoNbTaTiZr)C 0.8125 N 0.1875 . Oxygen preferentially occupies anion sites and substitutes for C more easily than N. The oxygen substitution energy varies by over 1.5 eV among local cation octahedra: Ti/Zr‐rich environments facilitate oxygen incorporation, while Mo/Nb/Ta‐rich configurations increase the oxygen substitution energy and suppress oxidation. Such environment dependence originates from competitive coupling of broken Me‒C/N networks, local lattice strain, and stabilization of newly formed Me‒O bonds. This work establishes an atomic‐scale framework for optimizing oxidation resistance via anion composition and cation short‐range order regulation, offering vital theoretical guidance.