0000000001130789
AUTHOR
Nai Phuan Ong
Crystal structure and physical properties of Mg6Cu16Si7-type M6Ni16Si7, for M=Mg, Sc, Ti, Nb, and Ta
Five compounds were investigated for magnetic character and superconductivity, all with non-magnetic nickel and band structures containing flat bands and steep bands. The syntheses and crystal structures, refined by powder X-ray diffraction, are reported for M{sub 6}Ni{sub 16}Si{sub 7}, where M = Mg, Sc, Ti, Nb, and Ta. All compounds form in the Mg{sub 6}Cu{sub 16}Si{sub 7} structure type. Resistance measurements are also reported on M{sub 6}Ni{sub 16}Si{sub 7} (M = Mg, Sc, Ti, and Nb) down to 0.3 K, with all four showing metallic conductivity. No superconductivity is observed. Magnetization measurements for all compounds reveal essentially temperature independent paramagnetism, with a tend…
Extreme sensitivity of superconductivity to stoichiometry in Fe1+?Se
The recently discovered iron arsenide superconductors appear to display a universal set of characteristic features, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in Fe1+?Se, which can be considered the parent compound of the superconducting arsenide family, is destroyed by very small changes in stoichiometry. Further, we show that nonsuperconducting Fe1+?Se is not magnetically ordered down to 5 K. These results suggest that robust superconductivity and immediate instability against an ordered magnetic state should not be considered as intrinsic characteristics of iron-based superco…