Characterization of Co-Substituted YBa₂Cu₃O_7-d Superconductors by Raman Spectroscopy —Application of Raman Spectroscopy to High-Tc Superconductors (1)—

We have investigated the phonon Raman spectra of YBa₂Cu_3-xCo_xO_7-d ceramic samples prepared by a polymerized complex method using Raman microprobe collection optics. Defect induced Raman scattering from Cu(1)-O(1) chains has been observed in Co-substituted samples, suggesting that Co predominantly enters the chain site. With increasing Co content the frequencies of the Ba, Cu(2), 0(2)-0(3) and the apex oxygen 0(4) vibrational modes along caxis change considerably. The changes are compared with those of interatomic bond distances as obtained by neutron diffraction and they indicate charge transfer effects between the CuO chain and the CuO₂ planes with increasing Co substitution. It is suggested that the O(4) mode is sensitive to small changes of the charge balance between the chain and the plane.