Applied superconductivity 1997, vols 1 and 2 issue:158 pages:1595-1598
We have performed a detailed analysis of the micro-Raman spectra obtained around the non superconducting Y2BaCuO5 (Y211) inclusions embedded in the bulk YBa2Cu3O7 (Y123) matrix of fast melt processed samples. The micro-Raman spectra have been recorded along lines crossing the Y211 inclusions with a resolution of 0.5 mu m. The energies of the Raman modes of the bulk Y123 matrix are higher than reported values which can be explained by the presence of accumulated compressive stress. Around the Y211 inclusions we observe, beside the appearance of the Raman modes of Y211, a softening of the Y123 Raman modes towards the reported values. The softening occurs in a similar way for all Y123 modes. This indicates a release of mechanical stress around the inclusions. The stress variations around Y211 inclusions can enhance the formation of micro cracks and so deteriorate the crystal For practical applications of the fast melt processed materials one should, besides optimizing pinning, provide also uniform mechanical properties around the pinning centers.