The Raman spectra of ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ ceramics with titanium concentration varying between $x=0.40\mathrm{}$ and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of the vibrational modes, we identified the boundaries among the rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of group theory analysis making possible the assignment of some modes for the monoclinic phase.

Polarized Raman and infrared espectra of l-threonine crystals have been obtained at room temperature and an assignment of normal modes is proposed based on group theory analysis. The usefulness of these assignments comes from the fact that some modes are related to important vibrations that can show changes under different pressure and temperature conditions.