Microstructure in High-Density ${\rm MgB}_{2}$ Wires Prepared by an Internal Mg Diffusion Method

Several reaction-induced diffusion processes to fabricate high-density MgB2 materials are developed, and the critical current density (Jc) has been notably enhanced. In this study, microstructure in high-density MgB2 wires fabricated by an internal Mg diffusion (IMD) process has been investigated. The inner reacted region of the wire heat-treated at 640°C for 1 h shows dense polycrystalline MgB2 of 20-200 nm in grain sizes. Fine MgO and Mg2Si particles of 10-30 nm in sizes are dispersed in this region. On the other hand, the outer region near the Ta sheath is composed of unreacted B and SiC powders, fine MgO particles and small voids. Sizes of voids in the IMD MgB2 wire are small compared with the PIT MgB2 wire. Oxidation of Mg in the IMD process forms fine dispersion of MgO which may be effective for flux pinning.

[1]  M. Reißner,et al.  Cu stabilized MgB2 composite wire with an NbTi barrier , 2010 .

[2]  H. Nakashima,et al.  Influences of Microstructure on Critical Current Properties in MgB_2 Superconducting Bulk Fabricated using a Premix-PICT Method , 2009 .

[3]  H. Kitaguchi,et al.  Superconducting properties of MgB2/Fe tape heavily doped with nanosized SiC , 2008 .

[4]  H. Sosiati,et al.  Microstructures of MgB2/Fe tapes fabricated by an in situ powder-in-tube method using MgH2 as a precursor powder , 2006 .

[5]  T. Ohnishi,et al.  Improvements in performance of focused ion beam cross-sectioning: aspects of ion-sample interaction. , 2004, Journal of electron microscopy.

[6]  S. Dou,et al.  Nanoscale-SiC doping for enhancing Jc and Hc2 in superconducting MgB2 , 2003, cond-mat/0308265.

[7]  H. Hatakeyama,et al.  Effect of SiO2 and SiC doping on the powder-in-tube processed MgB2 tapes , 2003 .

[8]  Rainer Wesche,et al.  High performance new MgB2 superconducting hollow wires , 2003 .

[9]  Australia.,et al.  Enhancement of the critical current density and flux pinning of MgB2 superconductor by nanoparticle SiC doping , 2002, cond-mat/0207223.

[10]  Jh H. Choi,et al.  High critical current density and enhanced irreversibility ® eld in superconducting MgB 2 thin ® lms , 2001 .

[11]  J. Nagamatsu,et al.  Superconductivity at 39 K in Magnesium Diboride. , 2001 .

[12]  P. Canfield,et al.  Superconductivity in dense MgB2 wires. , 2001, Physical review letters.

[13]  K. Togano,et al.  Fabrication of seven-core multi-filamentary MgB2 wires with high critical current density by an internal Mg diffusion process , 2008 .

[14]  H. Sosiati,et al.  TEM Analysis of Microstructures in Nano-sized SiC-doped MgB 2 Tapes , 2006 .