Atomic-Level Insights into the HfB ₂ Oxidation Mechanism by the Combination of Density Functional Theory and Ab Initio Molecular Dynamics Calculations

High-temperature oxidation of HfB2 governs its long-term stability in extreme environments, yet the atomistic dynamics of surface oxidation remain incompletely elucidated. Herein, the oxidation process of the HfB2(0001) surface was systematically investigated by combining density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The results show that O2 undergoes spontaneous dissociation on the Hf-terminated surface, forming a HfO2 layer that effectively suppresses further oxygen adsorption. In contrast, O2 dissociation on the B-terminated surface requires overcoming an energy barrier of 0.28 eV, and the resulting [BO3] units lead to surface structural degradation. AIMD simulations at 973 and 1673 K further demonstrate distinct reaction pathways: on the Hf-terminated surface, O atoms react exclusively with the surface Hf atoms; on the B-terminated surface, O atoms initially form B2O3 units, subsequently diffuse into the subsurface layer, and react with Hf atoms beneath the surface. This process involves reaction intermediates evolving sequentially from [HfB2O] to [Hf2B2O], then to [Hf3BO], and finally transforming into [Hf3O]. Notably, an elevated temperature accelerates oxygen diffusion and intermediate transformation, increasing the oxidation rate. These findings provide atomic-scale theoretical insights into HfB2 oxidation and establish a basis for optimizing the oxidation resistance.