Atomic-level insights into the initial oxidation mechanism of highentropy diborides by first-principles calculations

Understanding the initial oxidation mechanism is critical for studying the oxidation resistance of highentropy diborides. However, related studies are scarce. Herein, the initial oxidation mechanism of (Zr0.25Ti0.25Nb0.25Ta0.25)B2 high-entropy diborides (HEB2-1) is investigated by first-principles calculations at the atomic level. By employing the two-region model method, the most stable surface of HEB2-1 is determined to be (1120) surface. The dissociative adsorption process of the oxygen molecule on the HEB2-1-(1120) surface is predicted to proceed spontaneously, where O -O bond breaks and each oxygen atom is chemisorbed on the most preferable hollow site. The adsorption energy and the diffusion barrier of the oxygen atom on the (1120) surface of HEB2-1 are in the vicinity of the average level of the corresponding four individual diborides. In addition, ab initio molecular dynamics simulations indicate a high initial oxidation resistance of HEB2-1 at 1 000 K. Our results are beneficial to further designing the high-entropy diborides with excellent oxidation resistance. (c) 2023 The Author(s). Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).