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TT: Tiefe Temperaturen
TT 20: Postersitzung IV (Mesoskopische Systeme, Supraleitung: Massivmaterialien, Bandleiter, Pinning, Vortexdynamik, Transporteigenschaften, Korngrenzen)
TT 20.55: Poster
Donnerstag, 27. März 2003, 14:30–19:00, P2c, P2d
Influence of Mechanical Alloying Preparation Parameters on the Superconducting Properties of Nanocrystalline Bulk MgB2 and Powder in Tube MgB2 Tapes — •Olaf Perner, Andreas Gümbel, Jürgen Eckert, Günter Fuchs, Konstantin Nenkov, Karl-Hartmut Müller, Wolfgang Häßler, Claus Fischer, Bernhard Holzapfel, and Ludwig Schultz — Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, PO Box 270116, D-01171 Dresden, Germany
A series of nanocrystalline and highly dense bulk MgB2 samples prepared by mechanical alloying (MA) was investigated for the superconducting properties and possible application as precursor material for wires and tapes. Starting from the elements Mg and B in the stoichiometric ratio of 1 : 2, the formation was realized for different MA times receiving a partially reacted MgB2 powder. Short uniaxial hot pressing under vacuum led to highly densified nanocrystalline bulk samples with low impurity content. Resistivity measurements reveal that Tc and Hirr-to-Hc2 ratio depend strongly on the milling time. The same result was obtained for jc determined from dc magnetization loops. A 50 hours mechanical alloyed and subsequently annealed bulk sample showed the best superconductivity characteristics with Tc = 34.5 K, jc(7.5 K, 6.4 T) = 1·105 A/cm2 and Hirr ≅ 0.7 Hc2.
Hence for the fabrication of tapes using the powder−in−tube technique with either Cu or Fe as sheath material a 50 hours mechanically alloyed powder was chosen. The monofilaments annealed at 773 K achieved values of jc up to 4·105 A/cm2 in self−field at 4.2 K.