IR spectroscopy of the low-frequency phonon spectrum of the TbFe3(BO3)4 single-crystal

A study of the IR reflectance spectra of the TbFe3(BO3)4 crystal. We determined the frequencies of the polar lattice phonons in the high-temperature R32, and low- temperature P3121, phases. All 8A2 ⊕ 11E-modes were found in the high-temperature phase, with nine of them corresponding to lines of the absorption spectrum. In the low-temperature phase, of the 20A2 ⊕ 35E-modes allowed by the symmetry of the crystal lattice, 20A2 ⊕ 25E-modes were found.