Critical current density and flux pinning dominated by neutron irradiation induced defects in YBa sub 2 Cu sub 3 O sub 7 minus x

The functional dependence of critical current density ({ital J}{sub {ital c}}) upon defect density is studied with neutron irradiation of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}}. Identical polycrystalline samples of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} have been irradiated with fast neutrons ({ital E}{gt}0.1 MeV) in eight steps between 0 and 2.1 {times} 10{sup 18} n/cm{sup 2}. Critical current densities are obtained from magnetic hysteresis measurements and correlated with defect density measurements obtained from transmission electron microscopy. We observe that despite the existence of a significant degree of hysteresis in the as grown material the hysteretic {ital J}{sub {ital c}} in the irradiated samples appears to be dominated by a power law dependence on neutron fluence with an exponent of approximately 1/3 over a wide range of temperature, field and fluence.