Flux pinning in melt grown LRE123 superconductors

Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LRE: La, Nd, Sm, Eu, Gd) form a solid solution LRE_1+xBa_2–xCu₃O_y. When LRE123 superconductors are melt-processed in a reduced oxygen atmosphere, they exhibit high T_c's and large J_c values in high magnetic fields associated with a second peak effect. We believe that such a behavior is closely related to the presence of a LRE-Ba solid solution. In this paper we propose the flux pinning mechanism of LRE 123, and then discuss the source of the peak effect.