Bulk samples of MgxB2 with starting composition of x = 0.5 to 1.3 were prepared using a solid-state reaction route. Their structure and critical current density, JC, were investigated. The experimental results showed that the starting composition MgxB2, as well as the sintering temperature, had a significant influence on JC and Hirr. The lattice parameter a increased with x and c shows a maximum value around x = 0.9. All the samples possess a JC value about 106 A/cm2 in self-field for x > 0.5. However, at high magnetic field the Mg-deficient samples exhibited higher JC values. The highest irreversibility field of Hirr = 5.2T at 20K was reached for x = 0.8 with sintering temperature of 800C, which was 0.8T higher than that of the stoichiometric MgB2 sample. It was suggested that the formation of MgB4 nanoparticles was responsible for the increase of Hirr and JC.

Effect of Starting Composition and Annealing Temperature on Irreversibility Field and Critical Current Density in MgxB2. G.J.Xu, R.Pinholt, J.Bilde-Sørensen, J.C.Grivel, A.B.Abrahamsen, N.H.Andersen: Physica C, 2006, 434[1], 67-70