Phonon Raman Scattering of the Modulation-free (Bi, Pb)₂Sr₂(Ca, R)Cu₂O_z+aby Simultaneous Substitution of Bi by Pb and Ca by R (R: Rare earth-Y)

Phonon Raman spectra of the modulation-free Bi_{1. 2}Pb _{0. e}Sr ₂Ca _1-y, Cu ₂O. (0.2 ⪳y⪳0.8) have been investigated both in polycrystalline and single crystal forms. Polarized Raman spectroscopic measurements of single crystals made it possible to clarify some controversies on the Raman mode assignments for Bi₂Sr₂CaCu ₂O_8+d(Bi2212), most notably in high-frequency three prominent oxygen modes observed at 290, 460 and 630cm^-1, which we assigned to A_gO_B1+B_1gO_Cu, A_gO_Biand A_gO_apox, respectively. The energies of the three oxygen modes show drastic change with a decrease of the hole concentration: (1)A_gO_B1+ B _1gO_Cu. mode is shifted towards higher frequencies, (2)A_gO_Bimode hardly varies for y< 0.6, while softens for y=0.6, and A_gO_apox. P. mode is shifted towards lower frequencies. The observed changes in these oxygen modes are similar to those observed for the modulated Bi ₂Sr ₂Ca _1-yY_yT Cu₂O_Z. We propose that the Y/Ca substitution both in the modulated and modulation-free Bi2212 systems induced a hole filling on the CuO 2 plane, which can explain the behaviour of the oxygen modes observed in their Raman spectra.