Processing and Characterization of MgB2

A. SERQUIS; X. Z. LIAO

Frontiers in Superconductivity Research

Nova Science Publishers, Incorporated

Lugar: No Informado; Año: 2004; p. 73 - 97

We review our recent progress on the processing, structures and properties of MgB2. In particular, we have used a magnesium vapor infiltration process (MVIP) to make high quality MgB2 powder. We present detailed studies of the field and temperature dependence of the magnetization as well as scanning and transmission electron microscopy characterizations of samples prepared under different conditions. We compare the environmental stability, the critical current densities (Jc) and the creep relaxation rates of MgB2 samples with different microstructures. The MgB2 samples synthesized by MVIP were found to contain nanometer-sized Mg(B,O)2 precipitates. Magnetization data show that such precipitates act as effective flux pinning centers, without deteriorating other superconducting properties such as Tc. The sizes and distribution of these precipitates can be controlled through processing, providing an attractive way to introduce flux pinning centers. We also review our results on the effect of heat treatments on the microstructure, magnetization and transport properties of MgB2 wires prepared by the powder-in-tube method. We discuss the optimization of the annealing conditions that strongly improve the connectivity by eliminating most of the microcracks present in the un-annealed wires. On the other hand, hot isostatic pressed (HIPed) wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning.