Peculiarities of Raman Spectra Shape in the Disordered Ferroelectrics
  Theory of the first order Raman scattering (FOR) line shape allowing for nonlinear and correlation effects contribution to inhomogeneous broadening as well as dynamic mechanisms of homogeneous broadening is developed. It is shown that in general case FOR line contains two maxima, shape of low frequency one being defined by homogeneous broadening. Our theory explains the peculiarity of observed FOR scattering of TO_2 hard phonon in KTL and KTN at different temperatures and concentrations of Li and Nb ions. 
M. D. Glinchuk and I. V. Kondakova