Oxygen vacancies are one of the most important intrinsic defects in zinc oxide (ZnO), governing its electronic structure and functional properties in a wide range of applications, including catalysis, sensing, and optoelectronics. Controlling the formation and stability of oxygen vacancies is therefore a key strategy in ZnO defect engineering. In this work, we employ density functional theory (DFT) calculations to systematically investigate the effects of transition metal dopants, Fe and Cr, on oxygen vacancy formation in ZnO.

Fe and Cr atoms were introduced substitutionally at Zn sites in the ZnO lattice, and the structural stability and electronic properties of the doped systems were analyzed. Oxygen vacancy formation energies were calculated for pristine ZnO and Fe- and Cr-doped ZnO in order to quantitatively evaluate the impact of dopants on vacancy generation. In addition, electronic density of states (DOS) and charge density redistribution analyses were performed to elucidate the underlying electronic mechanisms responsible for changes in vacancy formation behavior.

The calculated results show that both Fe and Cr doping reduce the oxygen vacancy formation energy compared to pristine ZnO, indicating that oxygen-deficient configurations are energetically more favorable in the presence of transition metal dopants. This enhanced vacancy formation can be attributed to dopant-induced modifications in the local electronic structure. Specifically, Fe and Cr introduce localized d states that strongly interact with neighboring O 2p states, leading to substantial charge redistribution around the dopant sites. Upon oxygen removal, these dopant-related electronic states effectively accommodate the excess electrons, stabilizing the oxygen-deficient structure.

A comparison between Fe- and Cr-doped systems reveals distinct differences in their electronic behavior. While both dopants promote oxygen vacancy formation, Fe doping exhibits a more pronounced stabilization of the reduced ZnO lattice. This difference highlights the important role of dopant chemistry in determining defect energetics and electronic structure modulation.

Overall, this study demonstrates that Fe and Cr dopants are effective promoters of oxygen vacancy formation in ZnO through electronic structure stabilization and charge redistribution. The present work provides atomic-scale insights into transition metal–induced defect engineering in ZnO and offers fundamental guidelines for the rational design of defect-rich oxide materials.