Dresden 2003 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
TT: Tiefe Temperaturen
TT 10: Supraleitung: Massivmaterialien, Bandleiter, Pinning, Vortexdynamik, Transporteigenschaften, Korngrenzen II
TT 10.1: Hauptvortrag
Dienstag, 25. März 2003, 14:30–15:00, HSZ304
High Critical Fields and Currents in Mechanically Alloyed MgB2 — •Jürgen Eckert, Olaf Perner, 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 270016, D-01171 Dresden, Germany
The combination of high critical fields Hc2 and irreversibility fields of Hirr > 30 T and a critical current density jc of 3·106 A/cm2 at 4.2 K and 1 T in thin films render MgB2 promising for technical applications. However, in commercial powders and conventionally sintered polycrystalline MgB2 samples the above mentioned properties are reduced due to weak pinning. In contrast, mechanical alloying of elemental Mg and B powders at ambient temperatures combined with hot pressing yields high density nanocrystalline bulk samples with 40 − 100 nm sized grains and distinctly improved pinning. Resistivity measurements reveal that Tc, jc and the Hirr-to-Hc2 ratio depend strongly on the actual milling parameters. Optimizing milling and annealing conditions allows to prepare bulk specimens with a jc of about 7·105 A/cm2 at 10 K and Hirr of up to about 17 T. The improved pinning of this material is attributed to the large density of grain boundaries. The nanocrystalline MgB2 can be used as starting material for the preparation of tapes using the powder-in-tube technique with either Cu or Fe as sheath material. So far, monofilamentary tapes annealed at 773 K yielded jc values of up to 4·105 A/cm2 in self-field at 4.2 K. The microstructural and electrical properties will be discussed.