Comparison of superconducting and electronic properties of σ-and A-15 phase Nb?Al |
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Authors: | H R Khan Ch J Raub K Lüders Z Szücs |
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Institution: | 1. Forschungsinstitut für Edelmetalle und Metallchemie, D-7070, Schw?bisch Gmünd, Fed. Rep. Germany 2. Institut für Atom-und Festk?rperphysik, Freie Universit?t, D-1000, Berlin 33
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Abstract: | For both, the σ-phase and the A-15 phase structure of Nb−Al binary alloys the superconducting properties were investigated
in connection with measurements of normal state electronic properties like resistance and NMR-frequency and line width. The
A-15 phase shows a transition temperature ofT
c
≈17.5 K. The σ-phase shows only weak transitions at the same temperature which can be explained by A-15 inclusions in a non-superconducting
σ-matrix. The Al27-Knight shift at room temperature is reduced from 0.162% for pure Al to (0.024±0.002)% and (0.026±0.0025)% for the A-15 and
the σ-phase, respectively. The corresponding temperature coefficients differ in sign: positive for the A-15 and negative for
the σ-phase; this may have a relation to the different superconducting properties. The NMR line width and the resistance show
no different behaviour for the two phases. In general, the electronic properties seems to be less important for the occurance
of superconductivity in the Nb−Al system than the lattice structures. |
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Keywords: | 74 |
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