Raman spectroscopy as a unique tool for characterizing high-T_c superconducting oxides

We address our full attention to the various useful capabilities of the Raman scattering technique for characterizing high-T_c superconducting oxides. The powerful aspect of Raman spectroscopy is demonstrated with regard to detection of traces of impurities as compared with the conventional X-ray diffraction technique. Oxygen disordering within CuO chains in Co-doped Y123 type materials is sensitively detected by the Raman scattering technique, the degree of which is proportional to the intensity of the disorder induced Raman mode above 550 cm^-1. The phonon Raman spectra of (Pb₂Cu)Sr₂Y_1-xCa_xCu₂O_8+d, (Pb₂Cu)Sr_0.9La_1.1CuO_6+d and (Pb_0.5Cu_0.5)Sr₂YCu₂O_7+d are investigated and phonon assignments compatible with the layer stacking sequences found in these Pb-based cuprates are proposed. Raman scattering can also be used as a means to detect insulator-to-metal transitions in various high-T_c cuprates, an example of which is demonstrated for (Pb₂Cu)Sr₂Y_1-xCa_xCu₂O_8+d; the intensity for the B_1g O_Cu mode abruptly drops across the insulator-to-metal transition as a result of the increased metallic screening in the hole-introduced samples.