THE ROLE OF RADIATION-DAMAGE STRUCTURE AND FINE-SCALE PRECIPITATION IN THE PINNING IMPROVEMENT OF THERMAL-NEUTRON IRRADIATED LITHIUM FLUORIDE-DOPED YBA2CU3O7-X

The improvement of intragranular critical current density, j(c), and f lux pinning obtained by thermal neutron irradiation (fluences between 10(16) - 10(18) neutrons/cm(2)) in YBa2Cu3O7,(-x) doped with 8 mol% li thium fluoride (LiF) (YBCO-LIF) is explained by the occurrence of vari ous irradiation defects (point defect clusters, dislocation loops, sta cking faults) observed by transmission electron microscopy (TEM), A tw in fading process is also revealed accompanied by a lowering of the or thorhombicity index. At higher irradiation fluences (similar to 5 x 10 (17) 10(18) neutrons/cm(2)), a new mechanism related to the dispersion of fine Cu2O precipitates in the superconducting YBCO-LiF matrix coul d explain the enhancement of up to eight times obtained for j(c) value s. A good agreement between the dependence of the measured j(c) values on the applied magnetic field and the calculated curves, j(c) = f(B), derived from a theoretical model, previously proposed for the pinning contribution of fine particles dispersed in YBCO matrix, is obtained. The role of thermal neutron irradiation for the flux pinning improvem ent by introducing of strong pinning centers (irradiation defects and Cu2O microdispersoids) is also discussed. (C) 1998 Elsevier Science B. V. All rights reserved.