Effect of Composition on the Superconducting Transition Temperature of Tantalum Carbide and Niobium Carbide

Tantalum carbide and niobium carbide samples with carbon-to-metal molar ratios varying from 0.754 to 0.987 for tantalum carbide and from 0.70 to 0.977 for niobium carbide were examined for superconductivity. Both niobium and tantalum carbides were found to be superconducting with transition temperatures which vary with composition. The major conclusion is that the highest temperature is reached for the stoichiometric composition and any deviation therefrom results in a lowering and eventual disappearance (less than 1.05°K) of $T_c$.