Nanocrystalline ordered vanadium carbide: Superlattice and nanostructure
Abstract The crystal structure, micro and nanostructure of coarse and nanocrystalline powders of ordered vanadium carbide V8C7 have been examined by X ray and neutron diffraction and electron microscopy methods. The synthesized coarse crystalline powder of ordered vanadium carbide has flower like morphology. It was established that the real ordered phase has the composition V8C7 d (d 0.03) deviating from perfect stoichiometric composition V8C7. The vanadium atoms forming the octahedral environment #V6 of vacant sites in V8C7 d are displaced towards the vacancy The presence of carbon onion like structures was found in the vanadium carbide powders with a small content of free (uncombined) carbon. The nanopowders of V8C7 d carbide with average particle size of 20 30 nm produced by high energy milling of coarse crystalline powder retain the crystal structure of the initial powder, but differ in the lattice deformation distortion anisotropy.