Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 1: Superconductivity - Fabrication and Characterization

TT 1.5: Vortrag

Montag, 26. März 2007, 10:30–10:45, H18

Effect of different carbon dopants on the superconducting properties of mechanically alloyed MgB₂ — •Marko Herrmann¹, Wolfgang Häßler¹, Christian Rodig¹, Margitta Schubert¹, Manfred Ritschel², Bernhard Holzapfel^1,3, and Ludwig Schultz^1,3 — ¹Institute of Metallic Materials, IFW Dresden, P.O. Box: 270116, D-01171 Dresden, Germany — ²Institute for Solid State Research, IFW Dresden, P.O. Box: 270116, D-01171 Dresden, Germany — ³Dresden University of Technology, Department of Physics, D-01062 Dresden, Germany

Doping with carbon both in its elemental state as well as present within carbon compounds is the method of choice for enhancing the superconducting properties of MgB₂. Precursor powders of carbon-doped MgB₂ were prepared by mechanical alloying. This preparation, successfully applied at ambient temperature, produced nanocrystalline, partially reacted powders. The high reactivity of the milled powders promotes the formation of MgB₂ at reduced temperatures around 600^∘C to 650^∘C. Compared to other in-situ preparation techniques, bulk samples of undoped mechanically alloyed MgB₂ show a high J_c of 1 x 10⁶ A/cm² in self-field at 7.5 K and critical fields H_c2 of 20 T. This can be explained by the high density of grain boundaries, which act as pinning centers and enhance the critical current density remarkably. A comparison of promising carbon dopants like carbon nanotubes and silicon carbide is presented. We show the influence of these dopants on the critical transition temperature, lattice parameter, critical field and critical current density of bulk and tape samples.