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

✍ Scribed by J.P. Hodges; S. Short; J.D. Jorgensen; X. Xiong; B. Dabrowski; S.M. Mini; C.W. Kimball

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 607 KB
• Volume: 151
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8640

✦ Synopsis

Over the oxygen composition range 2.54x43.0, the SrFeO x system exists as four distinct compounds with the nominal composition Sr n Fe n O 3n؊1 (n ‫؍‬ 2, 4, 8, and R). The end member SrFeO 3 (n ‫؍‬R) possesses a simple cubic perovskite crystal structure, whereas the oxygen-de5cient (n ‫؍‬ 2, 4, and 8) members each adopt a di4erent vacancy-ordered perovskite crystal structure. Using time-of-6ight neutron powder di4raction, we show that previously proposed structures for the Sr 4 Fe 4 O 11 (n ‫؍‬ 4) and Sr 8 Fe 8 O 23 (n ‫؍‬ 8) compounds are incorrect. We determine the correct crystal structures for Sr 4 Fe 4 O 11 (orthorhombic, space group Cmmm, a ‫؍‬ 10.974(1) A > , b ‫؍‬ 7.702(1) A > , and c ‫؍‬ 5.473(1) A > ) and Sr 8 Fe 8 O 23 (tetragonal, space group I4/mmm, a ‫؍‬ 10.929(1) A > and c ‫؍‬ 7.698(1) A > ) through comparisons of the goodness of 5t for Rietveld re5nements 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 MoK ssbauer results for the same compounds. 2000