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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。
The MgB2 superconductors were prepared by the step reaction method using crystalline B powder and amorphous B powder respectively with Mg powder. The first step of the stepwise reaction method using different states of B powder and Mg powder by atomic ratio Mg: B = 1: 4 mixed for the doped sample plus 5%, 8% (mass fraction) of SiC, using 900 ℃, 30min or 800 ℃, 1h for high temperature heat treatment. The second step is to supplement the Mg powder, so that Mg: B = 1: 2, the mixed powder drawn through the tube after the second step 750 ℃, 2.5h heat treatment. The phase composition and microstructure of the samples were investigated by XRD and SEM. The I-V curve of the sample was measured by the standard four-lead method. The results show that a large amount of MgB4 with low reactivity can be formed during the first heat treatment of crystalline B powder and Mg powder. From the microstructure analysis, it is found that the samples prepared from the crystalline B powder have better grain connectivity and hence a more stable I-V relationship curve.