Melt-processed light rare earth element-Ba-Cu-O

Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution LRE_1+xBa_2-xCu₃O_y. The presence of such solid solution caused a depression in the superconducting transition temperatures (T_c), particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the T_c of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, J_c values of these superconductors were larger than that of a good quality Y123 superconductor in high magnetic fields at 77 K. In this article, on the basis of our study over the last several years, the melt processes for LRE-Ba-Cu-O are described, the microstructural and superconducting properties of the superconductors are reviewed and the flux pinning mechanism is also discussed.