THE ROLE OF Si AND C IN INFLUENCING THE CRITICAL PROPERTIES OF MAGNESIUM DIBORIDE SUPERCONDUCTOR

摘要

In this work, the effects of Si and C on the electrical transport and magnetic properties of polycrystalline magnesium diboride (MgB_2) superconductor were investigated. The temperature dependence of upper critical field, irreversibility field as well as the critical current density were measured. Analysis of the x-ray diffraction data indicated no substitution of Si into the lattice structure of MgB_2. Instead, Si reacted with Mg to form Mg_2Si which could act as scattering and flux pinning centers. On the other hand, Rietveld refinement of the lattice parameters showed a shrinkage in the α-axis of the hexagonal unit cell suggestive of C substitution on the B site. The contribution of the defects and C substitution on the critical properties is discussed. We demonstrate how impurity scattering in MgB_2 can be varied by control of reaction route. Ministry of Higher Education Malaysia: Exploratory Research Grant Scheme. X. Xu, K. S. B. De Silva, W. K. Yeoh and S. X. Dou, Institute for Superconducting and Electronic Materials, University of Wollongong, Australia. A. Kursumovic and J. L. MacManus Driscoll, Department of Materials Science and Metallurgy, University of Cambridge, U.K.