title: Evidence for Fe(2+) in wurtzite coordination: iron doping stabilizes ZnO nanoparticles.
abstract: First-principles calculations are used to investigate the structural and electronic properties of Fe-doped ZnO nanoparticles. Based on extensive validation studies surveying various density functionals, the hybrid functional PBE0 is employed to calculate the structures, formation energies, and electronic properties of Fe in ZnO with Fe concentrations of 6.25, 12.5, and 18.75 at%. Substitution of Zn by Fe, zinc vacancies, and interstitial oxygen defects is studied. High-resolution inner-shell electron energy loss spectroscopy measurements and X-ray absorption near-edge structure calculations of Fe and O atoms are performed. The results show that Fe-doped ZnO nanoparticles are structurally and energetically more stable than the isolated FeO (rocksalt) and ZnO (wurtzite) phases. The Fe dopants distribute homogeneously in ZnO nanoparticles and do not significantly alter the host ZnO lattice parameters. Simulations of the absorption spectra demonstrate that Fe(2+)  dominates in the Fe-doped ZnO nanoparticles reported recently, whereas Fe(3+)  is present only as a trace.
authors.affiliation: School of Engineering and Science, Jacobs University Bremen, Bremen, Germany.
authors.forename: Jianping
authors.initials: J
authors.lastname: Xiao
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Kuc
authors.forename: Suman
authors.initials: S
authors.lastname: Pokhrel
authors.forename: Marco
authors.initials: M
authors.lastname: Schowalter
authors.forename: Satyam
authors.initials: S
authors.lastname: Parlapalli
authors.forename: Andreas
authors.initials: A
authors.lastname: Rosenauer
authors.forename: Thomas
authors.initials: T
authors.lastname: Frauenheim
authors.forename: Lutz
authors.initials: L
authors.lastname: Mädler
authors.forename: Lars G M
authors.initials: LG
authors.lastname: Pettersson
authors.forename: Thomas
authors.initials: T
authors.lastname: Heine
mesh_terms: D007501:Iron / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D007501:Iron; D015034:Zinc Oxide