First-Principles Study of the Geometric and Electronic Structures of Zinc Ferrite with Vacancy Defect
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RECENTLY, zinc ferrite (ZnFe2O4) as one of the most widely studied ferrites has received great interest because of its excellent performance in many fields, such as gas sensors,[1] magnetic material,[2] adsorption,[3] photo-catalysis,[4] solar cells,[5] and lithium ion batteries.[6] ZnFe2O4 is also the main zinc-containing phase in the residue of zinc hydrometallurgy.[7,8] The structure of ZnFe2O4 consists of a cubic close-packed array of oxygen ions, with metal cations distributed in one eighth of tetrahedral interstices (A sites) and half of the octahedral interstices (B sites).[9] The bulk ZnFe2O4 is a normal spinel structure having the entire A (Zn2+) sites tetrahedrally coordinated and the B (Fe3+) sites octahedrally coordinated by oxygen atoms.[10] Generally, the ZnFe2O4 prepared in experiment or industrial production does not comprise perfect crystals, and some JINHUAN YAO, Associate Professor, and YANWEI LI, Professor, are with the Guangxi Key Laboratory of Electrochemical and MagnetoChemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin 541004, P.R. China. Contact e-mails: [email protected]; [email protected] XUANHAI LI, Professor, is with the School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, P.R. China. XIAODONG ZHU, Associate Professor, is with the Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150001, P.R. China. Manuscript submitted June 29, 2015. Article published online April 28, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
defects exist in the crystal structure. However, most experimental and theoretical studies have treated ZnFe2O4 as perfect crystals. Vacancy defect is a very typical lattice defect. Vacancy defect has a great influence on the geometric and electronic structures of the crystalline materials and, therefore, results in a change in physicochemical properties.[11–13] For example, Goya and Rechenberg[14] found that there exist oxygen vacancies and local disorder at Fe sites in ultrafine ZnFe2O4 particles obtained from mechanosynthesis of the precursor oxides. The oxygen vacancies and local disorder at Fe sites produced during milling could break the superexchange paths and induce spin disorder. Ponpandian and Narayanasamy[15] found that oxygen vacancies created by high-energy ball milling have an important influence on the electrical properties of nanocrystalline ZnFe2O4. ZnFe2O4 with the normal spinel structure is very stable, which severely hinders the effective recovery of zinc from the residue of zinc hydrometallurgy. Our previous studies also proved that the lattice defects produced by mechanical activation could reduce the stability of zinc ferrite and increase zinc leaching rate significantly.[16,17] However, it is difficult to investigate the precise effect of those vacancy defects on the microstructure and stability of zinc ferrite by using the experimental method. The first-principles calculations method based o
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