Abstract
Polarized Raman spectra of oriented single crystals have been studied in a broad temperature range (5–500 K) covering the crystallographic, ferroelectric, and magnetic transitions. From the spectra obtained at room temperature (RT) 10 out of the total 12 Raman active modes of the trigonal phase have been identified and assigned to definite atomic motions in close comparison to results of lattice-dynamics modeling. With the decrease in temperature below 250 K some Raman bands split, and additional spectral features, not expected for the structure, arise well above the magnetic transitions near 90 and 50 K. Their appearance, however, correlates with the transformation due to incommensurate structural modulation revealed by recent x-ray and neutron-diffraction studies. As temperature increases above RT the intensity of the Raman lines strongly decreases, and entering the high-temperature phase the spectrum transforms its shape to that expected for a structure with disordered Jahn-Teller distortions.
- Received 28 March 2014
- Revised 21 May 2014
DOI:https://doi.org/10.1103/PhysRevB.89.214302
©2014 American Physical Society