Reappearance of ferroelectric soft modes in the paraelectric phase of Pb(1-x)Ca(x)TiO3 at high pressures: Raman and x-ray diffraction studies

High pressure Raman spectroscopy and x-ray diffraction measurements have been carried out on Pb(1-x)Ca(x)TiO(3) (x = 0.10 and 0.30). Using high pressure Raman spectroscopic data, it is observed that the phonon instability responsible for the ferroelectric phase reappears in the paraelectric phase after a critical pressure. The observed critical pressures in the Ca(2+) doped PbTiO(3) system are much lower than the unique pressures suggested for PbTiO(3) based materials. A suitable explanation is given to explain this lowering of critical pressure. It is also shown that the ferroelectric phase which stabilizes in the paraelectric phase has a tetragonal symmetry with space group I4cm.