Nanostructure and atomic ordering in vanadium carbide

Nanostructured nonstoichiometric vanadium carbide VC0.87 was obtained in po wdered form using the ordering effect. The composition, structure, and prop erties of the carbide were studied by chemical and thermogravimetric analys is, gas chromatography, x-ray diffraction, optical and electronic microscop y, electron-positron annihilation, magnetic susceptibility, and microhardne ss methods. Nanostructured vanadium carbide VC0.87 possesses the crystal st ructure of the cubic ordered phase V8C7 with space group P4(3)32. Vanadium carbide nanocrystallites are shaped in the form of 400-600 nm in diameter a nd 15-20 nm thick curved petals. The surface layer of the nanocrystallites contains defects of the vacancy agglomerate type. The microhardness of vana dium carbide, obtained by vacuum sintering of VC0.87 nanopowder was 60-80 G Pa, which is 3-4 times greater than the microhardness of coarse-grained van adium carbide with the same composition and close to the hardness of diamon d. (C) 1999 American Institute of Physics. [S0021-3640(99)00906-8].