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

Understanding the initial oxidation mechanism is critical for studying the oxidation resistance of high-entropy 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 (112¯0) surface. The dissociative adsorption process of the oxygen molecule on the HEB2-1-(112¯0) 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 (112¯0) 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.