Tungsten carbide on the subnanoscale level: Atomic structure, electronic states, and mechanical properties

Density functional theory and pseudopotential methods are used to study the atomic structure, electronic states, and mechanical properties of WC nanoparticles 1 nm in size and smaller. It is found that the smallest particles (containing less than 15 atomic pairs of WC) have a cubelike NaCl-type structure. In the range of 10 to 20 pairs, WC particles with cubic and trigonal structures have approximately equal energies; however, their internal atomic structure preserves the alternation pattern of W and C atoms that is inherent in NaCl. A trigonal WC15 particle is used to study the tensile strength and resistance to compression. It is found that the strength of the nanoparticle is much higher than the strength of the bulk material. Tungsten and carbon vacancies decrease the strength of the particles; however, cobalt atoms penetrating into the vacancy positions can restore the strength of the nanoparticles and their resistance to compression almost to values characteristic of a defect-free case. The density of electronic states of WC nanoparticles has a form close to the density of states of the bulk cubic phase of tungsten carbide exhibiting a metallic nature with a high density near the Fermi level. © 2010 Pleiades Publishing, Ltd.