Modular Construction of Oxide Structures-Compositional Control of Transition Metal Coordination Environments.
The effects of reaction temperature and pO were investigated on a series of (Ba,Ca,Nd)FeO perovskite systems in order to isolate phases containing ordered arrangements of the distinct vacancy and cation ordering patterns identified in less compositionally complex iron oxide systems. Initial synthesi...
| Published in: | Journal of the American Chemical Society Vol. 130; no. 24; pp. 7570 - 7584 |
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| Main Authors: | , , , , , , |
| Format: | Article |
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American Chemical Society
6/18/2008
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| Online Access: | View this record in EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=34106848&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 34106848 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 6/18/2008 vid: 130 iid: 24 pid: 997 pub: American Chemical Society artinfo: ui: 34106848 10.1021/ja077762f ppf: 7570 ppct: 14 formats: tig: atl: Modular Construction of Oxide Structures-Compositional Control of Transition Metal Coordination Environments. aug: au: Tenailleau, Christophe Allix, Mathieu Claridge, John B. Hemeu, Maryvonne Thomas, Michael F. Hirst, James P. Rosseinsky, Matthew J. affil: Department of Chemistry, University of Liverpool, Liverpool, L69 7ZD, U.K Laboratoire CRISMAT-ENSJCAEN, UMR6508, 6 Bd du Maréchal Juin, 14050 Caen Cedex, France Department of Physics, University of Liverpool, Liverpool, L69 7ZE, U.K su: Oxide minerals Perovskite Cations Iron oxides Synchrotrons sug: subj: Oxide minerals Perovskite Cations Iron oxides Synchrotrons ab: The effects of reaction temperature and pO were investigated on a series of (Ba,Ca,Nd)FeO perovskite systems in order to isolate phases containing ordered arrangements of the distinct vacancy and cation ordering patterns identified in less compositionally complex iron oxide systems. Initial synthesis in air at high temperature yields cubic perovskite phases (I) with average iron oxidation states higher than 3; selected area electron diffraction together with diffuse features observed in the synchrotron X-ray diffraction (SXRD) patterns of these materials show evidence of small domains of short-range cation and vacancy order. Annealing these materials in nitrogen or in a sealed tube in the presence of an NiO/Ni buffer yielded the Fe phase CaBaNdFeO (II), closely related to SrLaFeO but with partial cation order as well as anion order present-the larger Ba cations are largely present in the 12-coordinate site between the octahedral iron layers, and Ca is largely present in 10-coordinate sites between octahedral and tetrahedral sites. Further reduction of CaBaNdFeO using a Zr getter yields the mixed-valence phase CaBaNdFeO (III). The structure of III was solved by maximum entropy analysis of XRD data coupled with analysis of high-temperature neutron diffraction data and refined against combined SXRD and high-Q ambient-temperature neutron data. This material crystallizes in a 20-fold perovskite super cell (Imma, a ~ √2×a, b ~ 10×a, c ~ √×2a) and can be visualized as an intergrowth between brownmillerite (CaFeO) and the YBaFeO structure. There are three distinct iron coordination environments, octahedral (O), square-pyramidal (Sp), and trigonal planar (Tp, formed by distorting the tetrahedral site in brownmillerite), which form a Sp-O-Tp-O-Sp repeat. Bond valence calculations indicate that Tp is an Fe site, while the O and Sp sites are Fe. The A-site cations are also partially ordered over three distinct sites: 8-coordinate between the Sp layers, 10-coordinate between Tp and O layers, and 12-coordinate between Sp and O layers. Mössbauer spectroscopy, magnetometry, and variable-temperature neutron diffraction show that the material undergoes two magnetic transitions at ~700 and 255 K. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2008 holdings: @attributes: islocal: N |
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