title: Insights into the effect of iron and cobalt doping on the structure of nanosized ZnO.
abstract: Here we report an in-depth structural characterization of transition metal-doped zinc oxide nanoparticles that have recently been used as anode materials for Li-ion batteries. Structural refinement of powder X-ray diffraction (XRD) data allowed the determination of small though reproducible changes in the unit cell dimensions of four ZnO samples (wurtzite structure) prepared with different dopants or different synthesis conditions. Moreover, large variations of the full width at half-maximum of the XRD reflections indicate that the crystallinity of the samples decreases in the order ZnO, Zn0.9Co0.1O, Zn0.9Fe0.1O/C, and Zn0.9Fe0.1O (the crystallite sizes as determined by Williamson-Hall plots are 42, 29, 15, and 13 nm, respectively). X-ray absorption spectroscopy data indicate that Co is divalent, whereas Fe is purely trivalent in Zn0.9Fe0.1O and 95% trivalent (Fe(3+)/(Fe(3+) + Fe(2+)) ratio = 0.95) in Zn0.9Fe0.1O/C. The aliovalent substitution of Fe(3+) for Zn(2+) implies the formation of local defects around Fe(3+) such as cationic vacancies or interstitial oxygen for charge balance. The EXAFS (extended X-ray absorption fine structure) data, besides providing local Fe-O and Co-O bond distances, are consistent with a large amount of charge-compensating defects. The Co-doped sample displays similar EXAFS features to those of pure ZnO, suggesting the absence of a large concentration of defects as found in the Fe-doped samples. These results are of substantial importance for understanding and elucidating the modified electrochemical lithiation mechanism by introducing transition metal dopants into the ZnO structure for the application as lithium-ion anode material.
authors.affiliation: School of Science and Technology, Geology Division, Camerino University , 62032 Camerino, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Giuli
authors.affiliation: CNR-Istituto Officina dei Materiali (IOM)-OGG , c/o ESRF-71, Avenue des Martyrs, 38043 Grenoble, France.
authors.forename: Angela
authors.initials: A
authors.lastname: Trapananti
authors.affiliation: Helmholtz Institute Ulm (HIU) , Helmholtzstraße 11, 89081 Ulm, Germany.|Karlsruhe Institute of Technology (KIT) , P.O. Box 3640, 76021 Karlsruhe, Germany.|Institute of Physical Chemistry, University of Muenster , Corrensstraße 28/30, 48149 Muenster, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Mueller
authors.affiliation: Helmholtz Institute Ulm (HIU) , Helmholtzstraße 11, 89081 Ulm, Germany.|Karlsruhe Institute of Technology (KIT) , P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: Dominic
authors.initials: D
authors.lastname: Bresser
authors.affiliation: CNR-Istituto Officina dei Materiali (IOM)-OGG , c/o ESRF-71, Avenue des Martyrs, 38043 Grenoble, France.
authors.forename: Francesco
authors.initials: F
authors.lastname: d'Acapito
authors.affiliation: Helmholtz Institute Ulm (HIU) , Helmholtzstraße 11, 89081 Ulm, Germany.|Karlsruhe Institute of Technology (KIT) , P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: Stefano
authors.initials: S
authors.lastname: Passerini