Abstract
First-principles molecular orbital calculations for ZnO with 3d transition-metal (TM) impurities ranging from Mn to Cu have been carried out in order to investigate the relationship between TM impurities and oxygen adsorption in ZnO ceramics. Two kinds of model calculations, i.e., the TM impurities with various formal charges in the bulk and oxygen atom adsorption on the (1010) surface with TM impurities, were performed. For bulk calculations, TM impurities form specific states within the band gap. The covalent bonding around TM impurities is reinforced by the increase in formal charges. A similar behavior is recognized for surface calculations. TM impurities at the surface are oxidized by the adsorbed oxygen atom and the covalent bonding around TM impurities is reinforced. On the other hand, the covalent bonding at the surface is weakened by oxygen adsorption when TM impurities are absent. This result suggests that TM impurities enhance oxygen adsorption at the ZnO surface. The mechanism may be similar at the grain boundary of polycrystalline ZnO.
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