title: Long- and Short-Range Structure of Ferrimagnetic Iron-Chromium Maghemites.
abstract: Maghemite-like materials containing Fe(3+) and Cr(3+) in comparable amounts have been prepared by solution-combustion synthesis. The conditions of synthesis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure iron maghemite since their maghemite-hematite transformation takes place at about ∼ 700 °C instead of ∼ 300 °C, as usually reported. These materials were studied by synchrotron radiation X-ray diffraction (XRD) and by X-ray absorption fine structure (XAFS) of the K-absorption edge of two elements. High-resolution XRD patterns were processed by means of the Rietveld method. Thus, maghemites were studied by XAFS in both Fe and Cr K-edges to clarify the short-range structure of the investigated systems. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure transitions were performed. The extended X-ray absorption fine structure (EXAFS) spectra were fitted considering the facts that the central atom of Fe is able to occupy octahedral and tetrahedral sites, each with a weight adjustment, while Cr occupies only octahedral sites. Interatomic distances were determined for x = 1, by fitting simultaneously both Fe and Cr K-edges average EXAFS spectra. The results showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense , 28040 Madrid, Spain (EU).|Centro de Investigación en Materiales DIP-CUCEI, Universidad de Guadalajara , Av. Revolución 1500, Col. Olímpica, Guadalajara, México.
authors.forename: Marco
authors.initials: M
authors.lastname: García-Guaderrama
authors.affiliation: Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31136, Chih, México.
authors.forename: María E
authors.initials: ME
authors.lastname: Montero-Cabrera
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense , 28040 Madrid, Spain (EU).
authors.forename: Emilio
authors.initials: E
authors.lastname: Morán
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense , 28040 Madrid, Spain (EU).
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Alario-Franco
authors.affiliation: Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31136, Chih, México.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Fuentes-Cobas
authors.affiliation: Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31136, Chih, México.
authors.forename: Edgar
authors.initials: E
authors.lastname: Macías-Ríos
authors.affiliation: Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31136, Chih, México.
authors.forename: Hilda E
authors.initials: HE
authors.lastname: Esparza-Ponce
authors.affiliation: Facultad de Ciencias Químicas, Universidad Autónoma de Chihuahua , Av. Escorza 900, Zona Centro, Chihuahua 31000, México.
authors.forename: María E
authors.initials: ME
authors.lastname: Fuentes-Montero