Raman study of crystal-field excitations in Pr2-xCexCuO4

Eleven Raman active crystal-field (CF) excitations involving 4f electrons are detected in Pr1.90Ce0.10CuO4 and Pr1.85Ce0.15CuO4. They correspond to transitions within the H-3(4), H-3(5) and H-3(6) multiplets and are associated with three types of inequivalent sites of the Pr3+ ion. There are unperturbed sites similar to those observed in Pr2CuO4. Next, there are perturbed sites, also reported previously for Pr2CuO4, whose concentration increases with cerium doping. The perturbation can be described by a local deformation identical to that observed earlier in the similar compound Nd2-xCexCuO4. This deformation is also presumed to be responsible for the 580 cm(-1) Raman active A(1g) local mode observed in Pr2CuO4 as well as in the other Ce-doped 214 cuprates. The third type of Pr3+ site, observed only in the Ce-doped compounds, is tentatively ascribed to local inhomogeneities provoked by trapped electrons. Also, in contrast to previous Raman and neutron studies, the pronounced 125 cm(-1) feature is found to be the low energy E-g symmetry phonon rather than a CF excitation. (C) 1999 Elsevier Science B.V. All rights reserved.