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H. Esna du Plessis, Johan P.R. de Villiers, Gert J. Kruger

Re-determination of the crystal structure of χ-Fe₅C₂ Hägg carbide

Keywords: Iron carbide, Haegg carbide, Powder diffraction structure analysis, X-ray diffraction, Electron diffraction

The crystal structure of χ-Fe₅C₂ Hägg carbide was re-determined using the simulated annealing capability of Topas Academic (Coelho, 2000). The unit cell is triclinic (space group P-1) with a = 11.5695(5) Å, b = 4.5713(2) Å, c = 5.0588(2) Å, α = 89.884(4)°, β = 97.765(3)° and γ = 89.964(5)°. The crystal structure was fitted by Rietveld refinement, resulting in R_wp = 8.19% and R_Bragg = 2.54%. The triclinic space group of χ-Fe₅C₂ Hägg carbide was determined using selected area electron diffraction (SAED). A TEM study was done to determine exposed crystallographic faces on coarse χ-Fe₅C₂ Hägg carbide particles. Energy calculations using Castep (Cambridge Sequential Total Energy Package, Payne, et al., 1992 and Milman et al., 2000) indicated the triclinic unit cell of χ-Fe₅C₂ Hägg carbide to have the same total energy as the monoclinic unit cell. Thermogravimetric analysis was used to characterize the carbon species in the sample.

Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0044-2968
Volume: 222, 05/2007
Pages: 211 - 217

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