Evolution of Oxygen-Vacancy Ordered Crystal Structures in the Perovskite Series SrnFenO3n−1 (n=2, 4, 8, and ∞), and the Relationship to Electronic and Magnetic Properties

• Published in: Journal of solid state chemistry Vol. 151; no. 2; pp. 190 - 209
• Main Authors: Hodges, J.P., Short, S., Jorgensen, J.D., Xiong, X., Dabrowski, B., Mini, S.M., Kimball, C.W.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.05.2000; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; CRYSTAL STRUCTURE; CUBIC LATTICES; ELECTRICAL PROPERTIES; Exact sciences and technology; Inorganic compounds; IRON OXIDES; MAGNETIC PROPERTIES; MATERIALS SCIENCE; OXYGEN; PEROVSKITE; Physics; STRONTIUM OXIDES; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; VACANCIES; VALENCE; Water, oxides, hydroxides, peroxides; Electronic properties; Inorganic compounds; Neutron diffraction; Transition element compounds; Moessbauer spectroscopy; Time-of-flight method; Perovskites; Experimental study; Nonstoichiometry; Strontium oxides; Powder pattern; Valence; Solid solutions; Crystallographic site; Chemical composition; Property structure relationship; Iron oxides; Magnetic properties; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1006/jssc.1999.8640

Over the oxygen composition range 2.5≤x≤3.0, the SrFeOx system exists as four distinct compounds with the nominal composition SrnFenO3n−1 (n=2, 4, 8, and ∞). The end member SrFeO3 (n=∞) possesses a simple cubic perovskite crystal structure, whereas the oxygen-deficient (n=2, 4, and 8) members each adopt a different vacancy-ordered perovskite crystal structure. Using time-of-flight neutron powder diffraction, we show that previously proposed structures for the Sr4Fe4O11 (n=4) and Sr8Fe8O23 (n=8) compounds are incorrect. We determine the correct crystal structures for Sr4Fe4O11 (orthorhombic, space group Cmmm, a=10.974(1) Å, b=7.702(1) Å, and c=5.473(1) Å) and Sr8Fe8O23 (tetragonal, space group I4/mmm, a=10.929(1) Å and c=7.698(1) Å) through comparisons of the goodness of fit for Rietveld refinements of candidate models and bond-length distributions for each model. Using the correct crystal structures, we are able to assign valence states to the Fe crystallographic sites and to achieve consistency with published Mössbauer results for the same compounds.