Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 1: Superconductivity - Fabrication and Characterization

TT 1.6: Talk

Monday, March 26, 2007, 10:45–11:00, H18

Correlation of Jc and microstructure in SiC added MgB₂ wires — •Balaji Birajdar¹, Nicola Peranio¹, Pavol Kováč², Wacek Pachla³, and Oliver Eibl¹ — ¹Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen, Germany — ²Institute of Electrical Engineering, Dúbravska cesta 9, 842 39 Bratislava, Slovakia — ³Institute of High Pressure Physics, Sokolowska 29/37, 01-142 Warsaw, Poland

Addition of SiC is known to enhance the critical current density (J_c) of MgB₂ wires. In this work, nano-crystalline SiC added MgB₂ wires are prepared by the powder-in-tube technique using different processing technologies. In ex-situ wires the powder is pre-reacted MgB₂+SiC and the annealing temperature is about 950 ^∘C. In in-situ wires the powder is Mg+2B+SiC and the annealing temperature is about 650 ^∘C. The J_c’s of the wires were found to differ by orders of magnitude. The best wires yielded a J_c of 10 000 A/cm² at B=9.7 T and T=4.2 K. Advanced electron microscopy techniques like EDX elemental mapping in SEM and TEM, and electron spectroscopic imaging (ESI) in TEM were used to study the microstructure of these wires on different length scales. The microstructure shows granularity (ex-situ samples) and incomplete phase formation (in-situ samples). Si is oxidised due to the high annealing temperature in ex-situ samples and forms Mg₂Si in in-situ prepared samples. C-doping of MgB₂ by dissolved SiC might play a role and would increase the B_c2 and J_c. Measurement of the C-content by SEM-EDX in MgB₂ is inaccurate, the minimum detectable mass fraction of C in MgB₂ is about 1.7 at.%.