Superconductivity of the Transition-Metal Carbides

By rapid quenching from the melt, solid solutions having the NaCl-type structure can be obtained between binaries of NbC, TaC, WC, and MoC. The superconducting transition temperatures of these pseudobinaries were investigated. The experimental results were consistent with the interpretation that the density of states at the Fermi surface is probably flat and that stoichiometry is the main factor for achieving the maximum in the superconducting transition temperature. Apparently, as the stoichiometry is improved, the attractive phonon interaction between electrons $V_{\mathrm{ph}}$ increases.