Lattice dynamics study of cubic Tb2O3

We report a joint experimental and theoretical study of the lattice dynamics of cubic Tb2O3. Up to 16 optical Raman‐active modes have been observed with polarized and unpolarized Raman scattering measurements on a high‐quality Tb2O3 single crystal. The measured wavenumbers have been compared with those of other rare‐earth (RE) and related sesquioxides with cubic (C‐type or bixbyite) structure. First‐principles calculations have allowed us to assign the symmetry of the experimentally observed Raman‐active modes. Additional lattice‐dynamical calculations on the related cubic RE sesquioxides Dy2O3, Gd2O3, Eu2O3, and Sm2O3 indicate that the phonon wavenumbers of the Raman‐active modes in these compounds are monotonically reduced with increasing the lattice parameter along the Dy2O3‐Tb2O3‐Gd2O3‐Eu2O3‐Sm2O3 series, thus prompting for a revision of the experimental Raman spectra of some of these compounds (mainly Eu2O3 but also Gd2O3). The lattice dynamics of cubic Tb2O3 is studied both experimentally and theoretically. Up to 16 optical Raman‐active modes are observed with Raman scattering measurements on a high‐quality single crystal. The measured wavenumbers have been compared with those of other cubic rare‐earth sesquioxides. Density functional theory lattice‐dynamical calculations on cubic Tb2O3 and also on cubic Dy2O3, Gd2O3, Eu2O3, and Sm2O3 predict a monotonic wavenumber reduction for the high‐wavenumber phonons along the Dy2O3‐Tb2O3‐Gd2O3‐Eu2O3‐Sm2O3 series. Our data and analysis suggest that the experimental Raman spectra of some of these compounds (mainly Eu2O3 but also Gd2O3) should be revised.