Synthesis, structure, and superconducting properties of tantalum carbide nanorods and nanoparticles

Tantalum carbide nanorods and nanoparticles have been synthesized using a vapor-solid reaction path starting with CVD grown carbon nanotube precursors. Their structures were studied using XRD, TEM, and HRSEM. Superconducting properties were characterized using a SQUID magnetometer. For reactions at lower temperatures, carbide nanorods, which replicate the similar to 14 nm diameter of the precursor carbon nanotubes, are observed. For higher temperature reactions, coarsened carbide nanoparticles (100-250 nm) are observed which have spherical or cubic-faceted 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 has a superconducting transition temperature of 9.7 K. In TaC nanorods and nanoparticles, the superconducting properties correlate with the lattice parameter. Nanoparticles with a little higher lattice parameter than the ideal one show higher T-c and higher fields at which the superconductivity disappears than stoichiometric bulk TaC.