Initial oxidation of ZrB₂(0 0 0 1) from first-principles calculations

The initial oxidation of ZrB₂ was investigated by density-functional theory (DFT) within the generalized gradient approximation to understand the atomistic adsorption mechanism. The oxidation reaction commences on ZrB₂ (0 0 0 1) surface with chemisorption of the on-surface oxygen molecule along the parallel and vertical channels. The results reveal that the plane of the adsorptive molecular oxygen is parallel to the ZrB₂ (0 0 0 1) surface at all the adsorption sites along all channels, and the adsorption state of the two O atoms of the oxygen molecule is the same after geometry optimization. Two stable adsorption structures are obtained when the oxygen coverage is 2/9 monolayer (ML). As oxygen coverage increases to 1/2 ML, the calculated adsorption energies can be classified into three types corresponding to three structures. The main difference of them results from the various state of the Zr atom bonding with the O atom. The Zr atom with stable twofold coordinated configuration and big O-Zr-O angle contribute most to the adsorption energy.