La-doped MgB2 superconductors with various doping levels (Mg1-xLaxB2; x = 0.00, 0.01, 0.03 and 0.05) were synthesized by using the solid-state reaction route at ambient pressures. Effects of La doping were investigated in relation to microstructural characteristics and superconducting properties, particularly the intragrain critical current density. The microstructural characteristics of the as-synthesized Mg(La)B2 compounds were studied employing the transmission electron microscopy. The latter investigations revealed inclusion of LaB6 nanoparticles within the MgB2 grains, which provide effective flux pinning centers. The evaluation of intragrain JC through magnetic measurements on the fine powdered version of the as-synthesized samples revealed that the JC values of the samples changed significantly with doping level. The optimum result on JC was obtained for Mg0.97La0.03B2 at 5K; JC reached ~1.4 x 107A/cm2 in self-field, ~2.1 x 106A/cm2 at 1T, ~2.5 x 105A/cm2 at 2.5T and ~1.8 x 104A/cm2 at 4.5T. The highest value of intragrain JC in the Mg0.97La0.03B2 superconductor was attributed to the inclusion of LaB6 nanoparticles, which were capable of providing effective flux pinning centers.

Effect of La Doping on Microstructure and Critical Current Density of MgB2. C.Shekhar, R.Giri, R.S.Tiwari, D.S.Rana, S.K.Malik, O.N.Srivastava: Superconductor Science and Technology, 2005, 18, 1210-4