Transport critical current in rare earth substituted superconductors RBa sub 2 Cu sub 3 O sub (7-delta)) (R=GD, Dy, Sm, Ho).

We have measured the transport critical current densities (J sub c) of various bulk polycrystalline RBa sub 2 Cu sub 3 O sub (7-delta) type high temperature superconductors R=Gd, (Dy, Sm, Ho, Y) at 77K as a function of magnetic field. The substitution of yttrium with magnetic rare earth elements resulted in no appreciable improvement or deterioration in the transport J sub c values (typically in the range 200-600 A/cm sup 2 at H=0). The similar J sub c values of all five barium cuprate compounds and their rapid deterioration in weak magnetic fields in a similar manner (J sub c 10 A/cm sup 2 at H=1000 gauss) suggest the possibility of generic "weak link" problems in these compounds.