  This work reports on the first Raman detection of the tetragonal to
monoclinic phase transition in PZT ceramics near morphotropic phase boundary at
low temperatures. The transition is characterized by changes in the frequency
of lattice modes with the temperature. The results presented here confirm the
previous one recently reported by Noheda et al. using high-resolution
synchrotron X-ray powder diffraction technique and dielectric measurements. The
stability of the new phase is discussed within the framework of
phenomenological Landau-Devonshire Theory.
