Different Pr3+ environments in Pr1.85Ce0.15CuO4: A Raman crystal-field excitation study

Abstract

Low-temperature Raman scattering of crystal-field (CF) excitations within the ${\mathrm{Pr}}^{3+}$ ground-state ${}_{}{}^3{}_{}{}^{}\mathrm{H}_4^{}{}_{}{}^{}$ multiplet of the compound ${\mathrm{Pr}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ suggests the presence of more than one CF environment for the ${\mathrm{Pr}}^{3+}$ ions. The Raman spectra were similar to spectra obtained in inelastic neutron-scattering experiments. The analysis of the Raman spectra for ${\mathrm{Pr}}_{1.85}$ ${\mathrm{R}}_{0.15}$ ${\mathrm{CuO}}_4$ samples with R=Pr, La, Y, Ce, and Th indicates three different environments for ${\mathrm{Pr}}^{3+}$. One is associated with charge transfer caused by the replacement of ${\mathrm{Pr}}^{3+}$ by the tetravalent ions ${\mathrm{Ce}}^{4+}$ or ${\mathrm{Th}}^{4+}$. A second is almost identical to that observed in ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$. The third is attributed to either an orthorhombic distortion or to sites of smaller lattice volume. The Nd- and Nd(Ce)-based compounds are also discussed.