Influence of Mg/B ratio and SiC doping on microstructure and high field transport Jc in MgB2 strands

• DOI: 10.1016/j.physc.2007.02.005
• Publication Date: 2007-02-21T12:16:43Z
• Authors: M.A. Susner; M.D. Sumption; M. Bhatia; X. Peng; M.J. Tomsic; M.A. Rindfleisch; E.W. Collings
• Keywords: 0103 physical sciences; 01 natural sciences

Abstract Improvements in B c2 , B irr , and high field transport J c s are crucial for many MgB 2 applications. As transport J c is inextricably linked with microstructure, a knowledge of the detailed influence of two of the most practical variables – Mg/B ratios and SiC additions – on microstructure, B c2 / B irr , and high field J c , is of interest. In this work, the influence of Mg/B ratios on microstructure, B irr , and transport J c was investigated in MgB 2 strands with and without SiC doping. The binary compositions chosen were Mg x B 2 where x = 0.85, 0.90, 1.0, 1.10, and 1.15 in monofilamentary strands. In general, high Mg molar percentages were seen to increase transport J c , especially at higher fields. At 8 T, for example, heat treatments at 700 °C for 40 min yielded J c s at 4.2 K which ranged from 5.8 × 10 3 A/cm 2 for x = 0.85 to 2.73 × 10 4 A/cm 2 at x = 1.15. Microstructures evolved from powdery (B-rich) to web-like (Mg-rich). In a second set of samples, Mg-rich stoichiometries were investigated with and without SiC. High field transport J c s increased, and the microstructure appeared to densify. Both excess Mg and SiC doping significantly increased high field J c . The highest transport result was seen for SiC dopant (5 mol%) added to 15% excess Mg strands, which yielded a transport J c at 4.2 K and 8 T of 5 × 10 4 A/cm 2 . Variable temperature analysis was performed on the 15% excess Mg strands with and without SiC in fields of 0–15 T. At temperatures below 20 K, excess Mg + SiC doping performed best, while above 20 K, excess Mg without SiC had better transport properties.