STRUCTURE AND SUPERCONDUCTIVITY OF Y(BA(1-X)R(X))(2)CU3O7-DELTA (R=LA,PR, AND ND)

Ponder X-ray diffraction and electrical-resistivity measurement were u sed to study the structure and the Te variation of Y(Ba(1-x)R(x))(2)Cu 3O7-delta (0 less than or equal to x less than or equal to 0.2; R = La , Pr, and Nd). The solubility limit was estimated as x 0.05, 0.075, an d > 0.2 with R = Nd, Pr, and La, respectively, which depends on the io nic radius of dopants. All three series undergo an orthorhombic-to-tet ragonal transition at x similar to 0.15-0.2. Meanwhile, the T-C increa ses slightly through a maximum at x similar to 0.025, then decreases r apidly with x, indicating an overdoped system for YBa2Cu3O7-delta. Whe reas, the normal-state resistivity increases with x for all temperatur e ranges. The similarities and differences nith various dopants are di scussed in conjunction with ionic size, valence change and hole-fillin g mechanism.