RAMAN-SCATTERING FROM AG AND B1G PHONONS IN BI2SR2CAN-1CUNO2N+4 (N = 1,2)

Raman measurements were performed on intergrowth-free Bi2Sr2CuO6+delta (2:2:0:1) and Bi2Sr2CaCu2O8+delta (2:2:1:2) crystals. The phonon spectra of both phases are similar; however, two lowest-frequency phonon lines corresponding to the 28- and 47-cm-1 lines in 2:2:1:2 were observed at 20 and 41 cm-1 in 2:2:0:1, and, in both cases, these two Raman features appear exclusively in the z(yy)zBAR configuration. In addition, two weak A(g) lines at 109 and 129 cm-1, which are absent in spectra of 2:2:0:1, were resolved for 2:2:1:2. An overall assignment can be achieved by attributing the two lowest-frequency lines to the first- and second-order scattering features of the amplitude mode of the super-structural modulation, and the other lines to the optical-phonon modes of the distorted orthorhombic subcell. A careful comparison between the spectra of the single- and double-CuO2-layer Bi compounds enables us to clarify some controversies on assignments of certain phonon modes, especially those in the CuO2 layer.