Superconductivity of the Transition-Metal Carbides

Abstract

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 V h increases.

A sharp change of Tc in polycrystalline NbxTa1–xCy and nanocrystals encapsulated in multiwall carbon nanocages

“…The data of a 0 as a function of x show small upward deviations from Vegard's law (not shown, but similar to Fig. 3 [8]). TEM using a TECNAI 30 (Philips) at 300 keV reveals the encapsulation of nanocrystals inside multiwall carbon nanocages (similar to Fig.…”

“…The NbC y -TaC y system has an advantage of a constant valence electron-atom ratio among alloyed interstitial carbides with the NaCl-type structure. In a study for Nb x Ta 1-x C y (0 6 x 6 1, y < 1) the regular variation of T c as a function of x has been explored [8], while our preliminary data exhibit a distinct change of T c around a 0 $ 0.446 nm. This substantial disagreement is a motivation of the present study.…”

“…The suppression of carbon vacancies in interstitial carbides as well as alloyed interstitial carbides of the transition elements with the NaCl-type structure has been an intriguing subject to be researched [1][2][3][4][5][6][7][8]. Following the Matthias's empirical model, the preparation and evaluation of superconducting compounds have been made [6][7][8]; the valence electron-atom ratio, the lattice volume, and the atomic mass are varied without any change of a constant crystal structure.…”

“…Following the Matthias's empirical model, the preparation and evaluation of superconducting compounds have been made [6][7][8]; the valence electron-atom ratio, the lattice volume, and the atomic mass are varied without any change of a constant crystal structure. The NbC y -TaC y system has an advantage of a constant valence electron-atom ratio among alloyed interstitial carbides with the NaCl-type structure.…”

Superhard Superconductive Composite Materials Obtained by High-Pressure-High-Temperature Sintering

“…The composites obtained in the reaction of diamonds with molybdenum are superconductors with characteristic features. First, the onset of the transition to the superconducting state is T C = 9.3 K, which is slightly lower than the T C values for molybdenum carbide obtained by sintering powders of molybdenum and graphite (Willens et al, 1967). Second, the transition width ∆T ≈ 5 K is larger than that for the diamond-niobium system.…”