Flux pinning in Y sub 1 minus x Pr sub x Ba sub 2 Cu sub 3 O sub 7 minus. delta. high T sub c superconductors

Magnetic relaxation measurements have been made on two sets of samples of Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} high {ital T}{sub {ital c}} superconductors with 0{le}{ital x}{le}0.10. The samples were prepared as fibers using a sol-gel process and as polycrystalline pellets using a standard solid-state reaction technique. In an applied field of 5 kOe at 30 K, the fluxoid pinning potential {ital U} was observed to increase approximately linearly with Pr concentration {ital x} at the rate {ital dU}/{ital dx}{approx}1 eV. A mechanism for the enhancement of {ital U} may be the suppression of the superconducting order parameter in the vicinity of the Pr ions due to magnetic pair breaking.