Effects of B Powder on the MgB2 Superconductor Prepared by Two-Step PIT

Abstract:

MgB2 superconductors were prepared by two-step PIT with B (crystalline or amorphous) and Mg as starting materials. The first step was mixing B (crystalline or amorphous) and Mg with the molar ratio of Mg:B=1:4. For the doping samples, 5wt% and 8wt% SiC were added to the mixture. Pressed pellets were treated at 900 oC for 30 min or 800 oC for 1 h. The second step was adding Mg to get the molar ratio of Mg:B=1:2. The tubes filled with the ground powders were treated at 750 oC for 2.5 h. The phase identities and the microstructure were investigated by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM), respectively. Voltage dependence of the current of MgB2 wire was measured by a standard four-probe method. The results demonstrate that lots of MgB4 in low energy is synthesized by crystalline B and Mg at the first step. The sample prepared from crystalline B exhibits an excellent grain connection and stable I-V characteristics.

Key words:MgB2 superconductor; two-step PIT; crystalline B; amorphous B