Abstract
The Raman and infrared phonons of isostructural rhombohedral and are studied at room temperature. The experimental spectra are compared with the prediction of lattice-dynamical calculations and the lines observed are assigned to definite atomic vibrations. It is shown that the Raman mode of symmetry in and (at and respectively) involves atomic motions that cause the rhombohedral distortion, i.e., it is a “soft” mode, and its position could be used as a measure of the degree of the distortion. It is also argued that the broad Raman bands in the high-frequency range of are not proper modes of the rhombohedral structure, but are rather induced by the dynamic Jahn-Teller effect.
- Received 10 August 1998
DOI:https://doi.org/10.1103/PhysRevB.59.4146
©1999 American Physical Society