G. W. Hull

Metal intercalation compounds of TaS2: Preparation and properties

We report the preparation of intercalation compounds of 2H–TaS2 with post transition period elements. In general we find that elements to the left of the metalloid line in the periodic table will intercalate TaS2. Crystallographic lattice parameters, the maximum amount intercalated per Ta, magnetic susceptibility, and superconducting transition temperatures are also given.

Properties of HxTaS2: Correlation between the superconducting Tc and an electronic instability in layer compounds

The preparation of HxTaS2 (0 < x < 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly H2O in air). Magnetic susceptibility data show that a low temperature transformation in 2H⋅⋅⋅TaS2 (at 80°K) is suppressed with the addition of hydrogen, and at the same time the superconducting transition temperature Tc rises from 0.8 to ∼4.2°K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and Tc measurements in other intercalation compounds, we suggest that the rise of Tc (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity.

Monodispersed tantalum disulfide and adsorption complexes with cations

Cathodic electrolysis of 2H⋅⋅⋅TaS2 in a dilute sulfuric acid electrolyte results in intercalation of hydrogen and water. The water content increases as the ionic strength of the electrolyte is decreased. Addition of neutral surfactants (1%−10% Triton X−705 or glycerol) followed by high−speed stirring gave TaS2 layers monodispersed in the aqueous surfactant. Electronic absorption spectra of the dispersions agree well with spectra of cleaved solids. Dyes were used to study adsorption on the layers. Only cationic dyes were adsorbed and the adsorption was determined to be due to an ion exchange reaction with protons. Solid adsorption complexes were prepared by ultracentrifugation of the dispersion or by adding dyes to undispersed, water swollen TaS2. The solid adsorption complexes gave no x−ray powder patterns, and were deficient in sulfur. Ac susceptibility measurements did not indicate bulk superconductivity in any of the complexes. Electron transfer from the TaS2 layers to reducible dyes was observed, the ...

Superconductivity in ternary Heusler intermetallic compounds

We report the discovery of superconductivity in a number of stoichiometric A2BC ordered ternary intermetallic alloys isostructural to the prototype ferromagnetic Heusler alloy, Cu2MnAl. Ni in the superconducting Ni2BC phases appears to be behaving as a full d-band constituent. The highest superconducting critical temperature Tc, for the Ni phases surveyed is exhibited by Ni2NbSn (Tc = 3.4 K).

Superconductivity in LaNi2Ge2 and related intermetallics

Abstract In this note, we report the discovery of superconductivity in LaNi2Ge2 (Tc = 0.69 K), isostructural to several new superconductors we have previously reported. In addition, we report limited solid solubility of Sn in several of the latter compounds and that Sn modestly raises Tc of these materials. Ni in LaNi2Ge2 is nonmagnetic.