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The formation of varieties of carbon ordering in pseudobinary compounds of V 2 C, Nb 2 C and Ta 2 C
Author(s) -
Hiraga K.,
Hirabayashi M.
Publication year - 1980
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889880011442
Subject(s) - crystallography , octahedron , chemistry , carbon fibers , lattice (music) , diffraction , metal , carbon atom , electron diffraction , materials science , crystal structure , physics , alkyl , organic chemistry , composite number , acoustics , optics , composite material
Ordering of carbon atoms in (V 1 − x Nb x ) 2 C, (Nb 1 − x Ta x ) 2 C and (V 1− x Ta x ) 2 C has been studied by electron diffraction. In addition to three basic structures of V 2 C (ζ‐Fe 2 N type), Nb 2 C and Ta 2 C [ anti ‐Cd(OH) 2 type], two superstructures are found at intermediate compositions of (V 1 − x Ta x ) 2 C. One of them appears also in (V 1 − x Nb x ) 2 C at x = 0.2–0.5 and the other in (Nb 1 − x Ta x ) 2 C at x = 0.1–0.5. In these five structures, carbon atoms are aligned along the c axis occupying alternate octahedral interstices in the h.c.p. metal cell. The existence conditions of these structures are interpreted by a pairwise interaction model regarding the carbon atom‐vacant interstice rows parallel to the c axis. The interaction energies for these rows up to the third‐neighboring pairs are estimated from diffuse‐scattering profiles observed on the specimens quenched from high temperatures. The results are discussed in comparison with the theoretical proposals for the ground‐state structures based on a triangular‐lattice gas model.