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

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Abstract
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.