Electronic Structure, Optical and Dielectric Spectroscopy Study of   TbMnO3
  Spectral ellipsometry studies of the optical functions, first observation of photoluminescence and low frequency dielectric permittivity investigations were performed in ferroelectric - multiferroic TbMnO3 single crystals. The main attention was paid to electronic band structure, nature of the main optical transitions and unusual behavior of the dielectric permittivity in the region of the sharp narrow temperature maximum, associated with ferroelectric phase transition. It was found that magnitude of the permittivity maximum decreases strongly with frequency, whereas position of maximum is frequency independent. Observed features of polarization response can be described satisfactorily in the frame of on the basis of the Landau-Khalatnikov theory for critical relaxation polarization 
V.A. Trepakov, A.G. Dejneka, O.E. Kvyatkovskii, D. Khvostova, Z.   Potucek, M.E. Savinov, L. Jastrabik, X. Wang and S.-W. Cheong
cond-mat.mtrl-sci