ラマン分光法による(Ca_xLa_1-x)(Ba_1.75-xLa_0.25+x)Cu₃O_7+δの局所構造変化の観察

抄録

Polycrystalline samples of (Ca_xLa_1-x)(Ba_1.75-xLa_0.25+x)Cu₃O_7+δ(CLBCO) tetragonal superconductor for x from 0.0 to 0.6 were studied by Raman scattering technique, which is sensitive to oxygen site symmetry in the high-T_c superconductors. On the Raman spectra, five extra modes at 200, 320, 400, 565 and 610 cm^-1, which did not appear on Raman spectra of tetragonal YBa₂Cu₃O₆, were observed. Based on the model that apical oxygen O(4) is displaced by La³⁺ on Ba site and the result of group theoretical analysis for this model, the 565 cm^-1 mode which possessed the strongest intensity among these extra modes could be assigned to another O(4) vibration. This indicates that O(4) is strongly attracted by La³⁺ on Ba site, resulting in a change of local structure.