Positron annihilation study on the stress-field pinning mechanism in (Eu,Y)-123 superconductors

The simultaneous measurements of Doppler-broadened radiation spectra and li fetime spectra have been performed on (Y1-xEux)Ba2Cu3O7-y (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1) superconductors. The mean lifeti me and S-parameter, respectively show a characteristic significantly symmet ric to Eu-doping concentration. Since lifetime and Doppler broadening spect roscopies are rather sensitive to the variation of the lattice distortion a nd defects induced by the stress-field of lattice mismatch, such symmetric behaviors of the S-parameter and the mean Lifetime suggest a striking chara cteristic of stress in Y1-xEux-123 superconductor. When the doping concentr ation x reaches 30%, the density of defects corresponding to stress-field a ppears the maximum, and there is an optimum distribution of the stress-fiel d so as to increase critical current J(c) in Eu-doped Y-123 superconductors , Our results of the critical current density obtained by means of measurem ents of susceptibility chi'(T,H-AC) and chi''(T,H-AC) also suggest that the enhancement of the critical current density to reach an optimum when Eu do ping x is 30%. We also qualitatively discuss experimental results in the fr amework of the model of stress-field pinning. The model calculating results also show the stress-field induced by lattice mismatch is an effective pin ning center, and further conform that the stress pinning mechanism is domin ant in RE-doped Y-123 superconductors, (C) 1999 Published by Elsevier Scien ce B.V. All rights reserved.