High pressure raman study of Bi-2212

The hydrostatic pressure dependence of the Raman spectra of Bi2Sr2CaCu2O8 single crystals has been investigated. The energy of the A(g) and B-1g modes was found to increase with pressure in agreement with previously reported measurements, except the strong mode at similar to465cm(-1), which softens with pressure, while another peak at similar to458 cm(-1) appears more pronounced at low temperatures and high pressures. The energy of both modes does not seem to change with increasing pressure, up to similar to5 GPa, although the average energy of the wide band has been found to soften, which is in disagreement with previously published results. Based on the modifications observed in some phonons at similar to1.8 GPa, which correlate with the reduction of T-c and the deformations of the CuO5 pyramids, we attribute the mode at similar to465 cm(-1) to the vibrations of the apex oxygen atoms. All modes due to the oxygen atoms were found to. be strongly anharmonic.