SYNTHESIS, STRUCTURE, AND SUPERCONDUCTING PROPERTIES OF TANTALUM CARBIDE NANORODS AND NANOPARTICLES

Tantalum carbide nanorods and nanoparticles have been synthesized usin g a vapor-solid reaction path starting with CVD grown carbon nanotube precursors. Their structures were studied using XRD, TEM, and HRSEM. S uperconducting properties were characterized using a SQUID magnetomete r. For reactions at lower temperatures, carbide nanorods, which replic ate the similar to 14 nm diameter of the precursor carbon nanotubes, a re observed. For higher temperature reactions, coarsened carbide nanop articles (100-250 nm) are observed which have spherical or cubic-facet ed morphologies. A morphological Rayleigh instability is postulated as initiating the transition from nanorod to nanoparticle morphologies. Stoichiometric bulk TaC crystallizes in the rock salt structure and ha s a superconducting transition temperature of 9.7 K. In TaC nanorods a nd nanoparticles, the superconducting properties correlate with the la ttice parameter. Nanoparticles with a little higher lattice parameter than the ideal one show higher T-c and higher fields at which the supe rconductivity disappears than stoichiometric bulk TaC.