In order to improve the extrinsic superconducting properties, a combination of nanocrystalline microstructure and particle doping was studied with regard to the enhancement of flux pinning. For comparison, MgO and SiO2 particles were separately introduced into the MgB2 matrix by using the in situ preparation technique of mechanical alloying. The oxides did not affect the formation of MgB2 but influenced the critical current density and the irreversibility field, Hirr, in hot-pressed bulk samples; due to a change in microstructure and lattice constants. The optimum doping levels were 5wt% for MgO and 2wt% for SiO2 additions, leading to improved JC values of 1.3 x 106 and 1.2 x 106A/cm2 in self-field at 7.5K, respectively, but did not affect the critical temperature. Microstructural investigations revealed a nanocrystalline MgB2 matrix with homogeneously distributed impurity particles.

Effects of Oxide Particle Addition on Superconductivity in Nanocrystalline MgB2 Bulk Samples. O.Perner, W.Hässler, J.Eckert, C.Fischer, C.Mickel, G.Fuchs, B.Holzapfel, L.Schultz: Physica C, 2005, 432[1-2], 15-24