Transport critical current in rare-earth-substituted superconductors R${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (R=Gd, Dy, Sm, Ho, Y)

We have measured the transport critical current densities ($J_c$) of various bulk polycrystalline R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$-type high-temperature superconductors (R=Gd,Dy,Sm,Ho,Y) at 77 K 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 $J_c$ values (typically in the range 200–600 A/${\mathrm{cm}}^2$ at H=0). The similar $J_c$ values of all five barium cuprate compounds and their rapid deterioration in weak magnetic fields in a similar manner ($J_c$<10 A/${\mathrm{cm}}^2$ at H=1000 gauss) suggest the possibility of generic ‘‘weak link’’ problems in these compounds.