B粉对分步法制备MgB2超导体的影响

通过分步反应法,利用晶态B粉和无定形B粉分别与Mg粉反应制备了MgB2超导体。其中分步反应法的第1步采用不同状态的B粉与Mg粉按原子比Mg:B=1:4混合,对于掺杂的样品另加5%,8%(质量分数)的SiC,采用900℃,30min或800℃,1h进行高温热处理。第2步是补充Mg粉,使Mg:B=1:2,均混的粉末经装管拉拔后进行第2步750℃,2.5h热处理。通过XRD、SEM研究样品的相组成、微观结构。采用标准四引线法测定了样品的I-V曲线。结果表明:晶态B粉与Mg粉可在第1步的热处理过程中生成大量低反应活性的MgB4。从微结构分析发现晶态B粉制备的样品具有更好的晶粒连通性,从而也得到了更稳定的I-V关系曲线。

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

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.