J c Enhancement in Melt Textured YBCO with Different 211 Content by Fast Neutron Irradiation

  • PDF / 86,404 Bytes
  • 4 Pages / 612 x 792 pts (letter) Page_size
  • 83 Downloads / 181 Views

DOWNLOAD

REPORT


Jc Enhancement in Melt Textured YBCO with Different 211 Content by Fast Neutron Irradiation Anke Köhler1, Jérôme Plain2, Wolfgang Seeböck1, Teresa Puig2, Anna E. Carrillo2, Harald W. Weber1, Xavier Obradors2 1 Atominstitut der Österreichischen Universitäten, Wien, A-1020, Austria 2 Institut de Ciència de Materials de Barcelona, C.S.I.C., Bellaterra, E-08193, Spain ABSTRACT Melt textured YBCO samples with and without 211 inclusions were irradiated by fast neutrons. The enhancement of the critical current density was studied as a function of the 211 content by means of SQUID magnetometry at temperatures from 5 to 77 K and magnetic fields from 0 to 8 T. The highest enhancement factor, found at 77 K and 1.5 T for a 211-free sample, is 27. The enhancement is less effective for samples with 211 inclusions. However, the critical current densities after irradiation show a similar temperature and field dependence in all samples. The role of the initial microstructure on the radiation effects is discussed.

INDRODUCTION Neutron irradiation typically enhances the critical current density in YBa2Cu3O7-δ (YBCO) bulk materials by one order of magnitude, since the created defects act as pinning centers. But the enhancement of Jc is not the same in all samples, because the initial microstructure influences the irradiation effect. The defects produced by neutron irradiation range from point defects to nm-sized amorphous regions [1], but the movement, the growth and the recovery of the newly created defects depend on the already existing defect structure. In melt textured samples we have to consider the oxygen distribution as well as the existence of additional phases, micro-cracks, grain boundaries, etc. The influences of oxygen annealing on the irradiation effect were already discussed in the case of single crystals [2] and further experiments are in progress. In this work we wish to concentrate on the influence of the Y2BaCuO5 (211) content in melt textured materials. EXPERIMENTAL DETAILS Melt textured samples with different 211 content were obtained by Top Seeding Growth [3]. For the preparation of the 211 free YBCO, BaZrO3 was used as an additive [4]. The oxidation of the samples was performed at 450 °C and at an oxygen pressure of ≈1 bar. The size of the samples is about 0.5×0.5×1.0 mm3. For the irradiation experiments, materials with a 211 content of 0 wt %, 15 wt %, 30 wt %, 39 wt % and 47 wt % were chosen. The starting materials were selected to show the highest possible Jc in order to avoid influences of micro-cracks and grain boundaries and to ensure optimal Jc conditions in the irradiated state. The critical current densities as a function of magnetic field were determined from magnetization loops at 45 K, 60 K and 77 K, measured by SQUID magnetometry in a SHE VTS magnetometer up to 8 Tesla. The field was applied parallel to the c-axis of the samples. For studying the temperature dependence of Jc in the self field, the samples were cooled in a II7.9.1

maximum field of 5 Tesla. Then the external field was removed and the