Abstract
The polarized Raman spectra of orthorhombic series were studied at room temperature. The variation of phonon frequencies with ionic radius as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing the stretching and bending modes strongly mix for to Tb, while for further decrease or the mode is observed at higher frequency than mode; (2) similar distortion-dependent mode mixing takes place for the rotational and modes. The mode mixing is particularly strong for the compounds with values close to the transition from type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational and modes scales to the angles of and rotations, respectively, and could be used as a measure of their value.
- Received 19 September 2005
DOI:https://doi.org/10.1103/PhysRevB.73.064302
©2006 American Physical Society