Effects of alloying on the superconducting properties of ErBa2 Cu3O7

In high-T_c superconductors, the low critical current densities in polycrystalline materials have been attributed to a combination of critical current anisotropy and poor superconducting coupling across grain boundaries. Theoretical calculations indicate that although the flux pinning should vary roughly inversely as grain size, the polycrystalline critical current behavior could possibly be understood in terms of stresses due to the grain boundary. Experiments have been conducted to increase the coupling between adjacent grains by modifying grain boundary chemistry. These include adding either a conducting layer or a superconducting layer at the interfaces. The effect of additions such as Ag, B, Bi, Ga, and In to produce a conducting layer and the alloying of RBa₂Cu₃O₇ with another superconductor to produce a superconducting layer were analyzed by measuring T _c and J_c and observing changes to the microstructure. Early results indicate some J_c enhancement with silver addition. However, the addition of a different superconductor appears more promising