Resonant Raman scattering of oxygen-deficient YBa2Cu3O7- delta : Evidence for the coexistence of ortho-I, ortho-II, and tetragonal microstructures.

The polarized Raman spectra of a single crystal of YBa 2 Cu 3 O 7-δ (δ∼0.6) at 15 K were studied using the 647.1, 568.2, 530.9, and 482.5-nm Kr + laser lines. The results give clear evidence for a multiphase scattering volume with the main microstructure phases corresponding to YBa 2 Cu 3 O 7 (OI), YBa 2 Cu 3 O 6.5 (OII), and YBa 2 Cu 3 O 6 (T). Significant differences in the frequencies of the OI-, T-, and OII-related modes, as well as variations of the mode intensities with hω L and scattering geometry, result in apparent shifts of the Ba, Cu(2), and O(4) lines