Lattice dynamics study of cubic Tb₂O₃

Abstract

Abstract We report a joint experimental and theoretical study of the lattice dynamics of cubic Tb 2 O 3 . Up to 16 optical Raman‐active modes have been observed with polarized and unpolarized Raman scattering measurements on a high‐quality Tb 2 O 3 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 Dy 2 O 3 , Gd 2 O 3 , Eu 2 O 3 , and Sm 2 O 3 indicate that the phonon wavenumbers of the Raman‐active modes in these compounds are monotonically reduced with increasing the lattice parameter along the Dy 2 O 3 ‐Tb 2 O 3 ‐Gd 2 O 3 ‐Eu 2 O 3 ‐Sm 2 O 3 series, thus prompting for a revision of the experimental Raman spectra of some of these compounds (mainly Eu 2 O 3 but also Gd 2 O 3 ).