Abstract
Abstract Polarized Raman spectra from superconducting (reduced) and non-superconducting (unreduced) single crystals of Nd 2− x Ce x CuO 4− y ( x =0.16) are presented. The spectra were measured at room temperature by the micro-Raman technique and with different exciting wavelengths. No differences between unreduced samples were detected. Four Raman modes with well characterized polarization properties are found. They are compound with the predictions of factor group analysis of the undoped compound. The A 1g mode at 229 cm -1 which corresponds to out-of-phase motions of the Nd 3+ ions shows a resonant behavior at about 2.4 eV that we ascribe to electric transitions among the 4f 3 electronic levels of the Nd 3+ ion. The modes at 333 (B 1g ) and 475 (E g ) cm -1 are assigned to motions of the oxygens which are not in CuO 2 planes. The strong feature at 585 cm -1 has a clear A 1 character and is interpreted as being due to an IR mode associated with the motion along the c -axis of the oxygens in the CuO 2 planes, which becomes Raman active by the presence of the Ce impurity.
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