Effect of la doping on microstructure and critical current density of MgB2

Abstract

In the present study, La-doped MgB2 superconductors with different doping levels (Mg1-xLaxB2; x ≤ 0.00, 0.01, 0.03 and 0.05) have been synthesized by the solid-state reaction route at ambient pressure. Effects of La doping have been investigated in relation to microstructural characteristics and superconducting properties, particularly intragrain critical current density (Jc). The microstructural characteristics of the as-synthesized Mg(La)B2 compounds were studied employing the transmission electron microscopic (TEM) technique. The TEM investigations reveal inclusion of LaB6 nanoparticles within the MgB2 grains, which provide effective flux pinning centres. The evaluation of intragrain Jc through magnetic measurements on the fine powdered version of the as-synthesized samples reveal that Jc values of the samples change significantly with the doping level. The optimum result on Jc is obtained for Mg 0.97La0.03B2 at 5 K; Jc reaches ∼1.4 × 107 A cm-2 in self-field, ∼2.1 × 106 A cm-2 at 1 T, ∼2.5 × 10 5 A cm-2 at 2.5 T and ∼1.8 × 104 A cm-2 at 4.5 T. The highest value of intragrain Jc in the Mg0.97La0.03B2 superconductor has been attributed to the inclusion of LaB6 nanoparticles, which are capable of providing effective flux pinning centres. © 2005 IOP Publishing Ltd.