First-Principles Study of the Geometric and Electronic Structures of Zinc Ferrite with Vacancy Defect

The effects of Zn-vacancy (Zn₇Fe₁₆O₃₂), Fe-vacancy (Zn₈Fe₁₅O₃₂), and O-vacancy (Zn₈Fe₁₆O₃₁) on the geometric and electronic structures of normal spinel ZnFe₂O₄ (Zn₈Fe₁₆O₃₂) are studied by using a first-principles method based on density functional theory (DFT) at a generalized gradient approximation (GGA) level. Compared with perfect ZnFe₂O₄, the lattice parameters of ZnFe₂O₄ with Zn-vacancy or Fe-vacancy increase slightly, while the lattice parameters of ZnFe₂O₄ with O-vacancy decrease significantly. All the vacancy defects induce the distortion of the unit cell structure, especially for the O-vacancy. Zn-vacancy, Fe-vacancy, and O-vacancy in ZnFe₂O₄ cannot be formed spontaneously, but Zn-vacancy is the most prone to form, followed by Fe-vacancy and O-vacancy under the condition of external energy supply. Zn-vacancy, Fe-vacancy, and O-vacancy change the properties of ZnFe₂O₄ from a semiconducting character to a metallic character. Either ZnFe₂O₄ or ZnFe₂O₄ has various vacancy defects, the strength of the O-Zn bond is stronger than that of the O-Fe bond, and both of them have a covalent bond character. Zn-vacancy enhances the strength of O-Fe bonds and slightly weakens the strength of O-Zn bonds around Zn-vacancy. Fe-vacancy induces a significant increase of the strength of O-Fe bonds and O-Zn bonds around Fe-vacancy. O-vacancy leads to a significant decrease in the strength of O-Zn bonds and to a slight increase in the strength of O-Fe bonds around O-vacancy.