PHONON-SCATTERING SPECTRA OF (EU2/3CE1/3)2(BA2/3EU1/3)2CU3O9 AND (ER2/3CE1/3)2(BA2/3LA1/3)2CU3O9

Raman-scattering spectra of (Eu2/3Ce1/3)2(Ba2/3Eu1/3)2Cu3O9 and (Er2/3Ce1/3)2(Ba2/3La1/3)2Cu3O9, both of which have Cu-O5 pyramid structure, as well as YBa2Cu3O7, have been observed at room temperature with use of single crystals. A scattering peak with B1g symmetry has been observed at around 180 cm-1 and peaks with A1g symmetry at around 220, 290, 450, and 540 cm-1, in both compounds. The 180-cm-1 peak with B1g symmetry is assigned to the out-of-phase bending of oxygen in the Cu-O2 plane and the 540-cm-1 peak with A1g symmetry to the stretching of apical oxygen. Phonon-energy calculation has been performed with use of ionic potentials obtained for YBa2Cu3O7. To explain the observed B1g phonon energies, it has been found that the polarizability of the oxygen in the Cu-O2 plane in these compounds must be increased in relation to that in YBa2Cu3O7. The 220- and 290-cm-1 peaks are tentatively assigned to the mixed vibrational modes of oxygens in the Cu-O2 plane and lanthanide atoms.