PHONONS IN ND2-XCEXCUO4

We have measured far infrared reflection and Raman spectra on high quality single crystals and ceramic samples of the Nd2-xCexCuO4 system. The TO and LO frequencies of all infrared-active phonons were determined from a Kramers-Kronig analysis of the infrared reflection spectra. The frequencies of the detected Raman-active phonons are 228 cm-1 (A1g Nd), 328 cm-1 (B1g O2) and 480 cm-1 (Eg 02). A resonantly enhanced peak at 580 cm-1 is observed for Ce-doped samples only with polarization properties like an A1g phonon. We have also performed lattice-dynamical calculations with parameters extracted from those of perovskites and metallic oxides. The frequencies obtained agree well with our experimental findings. We present the eigenvectors of all zone center phonons. Finally, we also detected a feature at 165 cm-1 in the a b-polarized infrared spectra in Nd2CuO4 which might be of magnetic origin. © 1990.