Raman-active phonons in Bi 2Sr 2Ca n−1 Cu nO 2 n+4 d ( n=1,2,3) – phonon assignment and charge redistribution effects

Abstract

The phonon Raman spectra of Bi 2Sr 2Ca n−1 Cu n O 2 n+4 d ( n=1,2,3), high- T c superconductors have been investigated in a number of single-crystal and polycrystalline samples. From the polarization and doping dependence, and from a comparison with previous reports on other high- T c cuprates, we identify the A 1g and B 1g symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. On the basis of the assignments proposed here, we discuss the influence of aliovalent substitutions on the phonon modes in Bi 2Sr 2− x La x CuO 6+ d and Bi 2Sr 2Ca 1− y Y y Cu 2O 8+ d . We interpret the observed changes in phonon frequencies and intensities as a combination of internal pressure and charge redistribution effects induced by doping.