Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution LRE1+xBa2-xCu3Oy. The presence of such solid solution caused a depression in the superconducting transition temperatures (Tc), particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the Tc of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, Jc 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.
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