Raman spectroscopic study of phase transitions in undoped morphotropic PbZr 1-x TixO3

Several PbZr1-xTixO3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr1-xTixO3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions