date:Katholieke Univ Leuven, Vaste Stof Fys Magnetisme Lab, B-3001 Louvain, Belgium; Int Superconduct Technol Ctr, Superconduct Res Lab, Div 7, Minato Ku, Tokyo 105, Japan
We have performed a detailed analysis of the micro-Raman spectra recorded around the non-superconducting R2BaCuO5 inclusions embedded in different melt grown RBa2Cu3O7 (R = Y, Nd) samples. The Raman spectra were recorded every 0.4 or 0.5 mu m along a line crossing one or more inclusions on two specific samples. Sample A, YBa2Cu3O7 With 33 vol% of Y2BaCuO5 was prepared following a fast-melt-processing scheme. The cooling rate of the melt, crossing the peritectic temperature, was 180 degrees C/h. We observed a downshift of the phonon modes of the superconducting phase around the inclusions. This softening can be related to the presence of tensile stresses around the inclusions. Sample B, NdBa2Cu3O7 With 40% Of Nd4Ba2Cu2O10 was Prepared following an oxygen-controlled-melt-growth method. A cooling rate of 1 degrees C/h was applied to produce this sample. In this case we found a hardening of the phonon modes of the superconducting phase around the inclusions towards the energy of the phonon modes obtained in single crystals. Again, this shift of the Raman peak position can be related to the variation of mechanical stress around the inclusions. The hardening can be caused by the relaxation of tensile stress in the superconducting matrix around the inclusions. (C) 1998 Elsevier Science Ltd. All rights reserved.