Abstract
When evaporated C/Fe/C sandwich films prepared by successive vacuum evaporation were heated in vacuum below 620 K for more than 16 h, a new iron carbide named as τ1 was formed, and when a mixture of iron and carbon powders was heated at 1870 K in a stream of hydrocarbon gas, the carbide τ1 and another new iron carbide named as τ2 were formed. The carbide τ1 takes a morphology of very thin plate. Patterson-Fourier method was applied to electron diffraction structure analysis. The result showed that the crystal is trigonal with lattice parameters a=0.5286 and c=0.34±0.5 nm, and belongs to the space group P\bar31m. The composition is FeC3. Fe is at the position 2c, and C at 6k with x=0.33 and z=0.25. On the other hand, the carbide τ2 is cubic with lattice parameter a=0.784 nm, and belongs to the space group Fm\bar3m. The composition is Fe2C7. Fe is at the position 8c, and C at 4b and 24d. In both of the structures, each Fe atom is surrounded by six C atoms making an octahedrons.
