Reinvestigation and superstructure of La{sub 3.67}[Fe(C{sub 2}){sub 3}]
- Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Str. 40, 01187 Dresden (Germany)
The lanthanum iron carbide La{sub 3.67}[Fe(C{sub 2}){sub 3}] was prepared from the elements by argon arc-melting followed by annealing. The crystal structure of the ternary phase was reported previously (space group P6{sub 3}/m with a=878.7(2) pm, and c=535.1(1) pm) [A.M. Witte, W. Jeitschko, Z. Naturforsch. 51b (1996) 249-255]. In the present work the compound was reinvestigated by X-ray powder and single crystal diffraction, and was further characterized by metallographic methods and chemical analyses. Our diffraction data clearly reveal a superstructure with weak superstructure reflections in the space group P6{sub 3}/m with a=879.26(8) pm and c=1604.59(15) pm, thus tripling the previously reported subcell. The crystal structure (refinement to R1=0.044 and wR2=0.075 for 1387 unique reflections and 60 variables) contains Fe(C{sub 2}){sub 3} trigonal planar groups with the C{sub 2} ligands bonded end-on to the Fe atoms. The C-C distance is typical for a double bond. La atoms as the least electronegative component surround the complex anions and form a framework of face-sharing tricapped trigonal prisms. The resulting hexagonal channels at 0, 0, z of the partial structure with chemical composition La{sub 3}FeC{sub 6} are occupied by four additional La atoms per unit cell. These La atoms are fully ordered within a linear chain and display a Peierls-like distortion pattern. However, no long-range order in the a-b plane has been observed due to the random orientation of the chains. Because of the two different orientations which are possible for each chain the situation is similar to an Ising model on a triangular lattice. - Graphical abstract: Diffraction data reveal a superstructure with weak superstructure reflections for La{sub 3.67}[Fe(C{sub 2}){sub 3}] in the space group P6{sub 3}/m. The superstructure is caused by an ordered arrangement of La atoms along 0, 0, z with alternating short and long distances.
- OSTI ID:
- 21370418
- Journal Information:
- Journal of Solid State Chemistry, Vol. 182, Issue 6; Other Information: DOI: 10.1016/j.jssc.2009.01.040; PII: S0022-4596(09)00047-4; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANNEALING
ARGON
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
HEXAGONAL LATTICES
IRON CARBIDES
ISING MODEL
LANTHANUM COMPOUNDS
MELTING
METALLOGRAPHY
SPACE GROUPS
X-RAY DIFFRACTION
CARBIDES
CARBON COMPOUNDS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL MODELS
CRYSTAL STRUCTURE
DIFFRACTION
ELEMENTS
FLUIDS
GASES
HEAT TREATMENTS
IRON COMPOUNDS
MATHEMATICAL MODELS
NONMETALS
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS
RARE GASES
SCATTERING
SYMMETRY GROUPS
TRANSITION ELEMENT COMPOUNDS