Effects of precursor powders and sintering processes on the superconducting properties of MgB₂

Abstract

Different precursor powders and procedures were used to fabricate MgB2 superconductor. It was found that the purity of the B powder had strong effects on the Tc and Jc of MgB2. The Jc of the sample made from 90% B powder decreased 40 times at 3 T and 20 K compared with the 99% B powder samples. The impurity phases might be the reason for the suppression of the Tc and the Jc. Variation of the Mg:B ratio also influenced the MgB2 properties. Jc decreased with fluctuations from the normal rate (Mg:B = 1:2). It was found that the effects of the oxidization of the Mg powder on Jc were not strong when the Mg powder was only slightly oxidized. However, when the Mg powder was severely oxidized, the Jc decreased significantly. A two-step sintering process was adopted to make MgB2. In this process, the first sintering stage was at a lower temperature. It was found that this pre-sintering did not have a good effect on the properties, despite the fact that the mass density was improved. The phase composition and microstructure were analysed to explain the different effects.