Resistivity, Superconductivity, and Order-Disorder Transformations in Carbides and Carbohydrides

Abstract

The object of the study was to investigate electron transport in transition-metal carbides with special attention to ordering effects in substoichiometric carbides and to the influence of hydrogenation.

The superconducting transition temperatures of partially ordered Nb(,6)C(,5) and hydrided NbC(,x) were decreased from those of the original specimens, disordered NbC(,.83) and NbC(,x), respectively. The normal state resistivity of Nb(,6)C(,5) displayed the "bulge" in its temperature dependence characteristic of high T(,c) superconductors. Hydrided carbide specimens showed reduced resistivity values, a result attributed to the reduction of defect scattering as the carbon vacancies are filled with substitutional hydrogen ions.

The effect of the order-disorder transformation NbC(,.83) = Nb(,6)C(,5) at 1030(DEGREES)C was to reduce defect scattering also, as the carbon vacancies became incorporated into the periodic potential of the ordered phase.

New data on the normal state resistivity and superconducting transition of single crystal NbC(,.98) and TaC(,.98) are reported. Resistivity results for non-superconducting HfC(,.97) and WC crystals are also given.