Pressure-induced low symmetry phases in Ti-rich lead zirconate titanate PbZr0.20Ti0.80O3

The titanium--rich PZT solid solution PbZr0*20Ti0*80O3 was studied under high pressure by X--ray diffraction and Raman spectroscopy. A series of low--symmetry phases were observed, including monoclinic (space groups Cm and Cc) and triclinic forms (space groups F1 and F1*?) in PbZr0*20Ti0*80O3. High pressure Raman spectra obtained are consistent with a monoclinic (Cc)--triclinic (F1) phase transition involving a soft mode at 9GPa, in agreement with the change in compressibility detected by X--ray diffraction. The strong Raman spectra observed in the paraelectric phase can also be explained by the triclinic F1*? symmetry.