Raman spectroscopy of single crystals of high-Tc cuprates

We present normal mode assignments for the Raman spectra of 1–2–3-type materials on the basis of polarized Raman studies of single crystals of Ba2YCu3O7, Ba2YCu3O6, Sr2YCu2.4Al0.6O7, and Ba2−xLa1+xCu3O7+δ. In Ba2YCu3O7 we observe five intrinsic modes at 500 [O(1) axial stretch], 435 [in-phase O(2), O(3) bend], 335 [out-of-phase O(2), O(3) bend], 140 [Cu(2) axial stretch mode], and 118 cm−1 (Ba axial mode). Defect-induced modes are found at 600 and 220 cm−1. A mode at 640 cm−1, which is seen only in ceramics, is shown to be due to a BaCuO2 impurity phase. Furthermore, we discuss the Raman spectra of Bi2Sr2Can−1CunO4+2n and the high-frequency (ω > 1000 cm−1) scattering in Ba2YCu3O6 and Ba2YCu3O7.