Second harmonic generation and high pressure ferroelectricity in PbTiO$_{3 }$(II)*

We employed the Raman scattering, x-ray diffraction, and second harmonic generation (SHG) experiments to investigate the behavior of PbTiO$_{3}$ under pressure up to 100 GPa at 300 K. The experimental results reveal that lead titanate undergoes a second order phase transition from a tetragonal to a cubic at 12 GPa and continuously to a non-cubic structure at 30 GPa. The integral intensity of SHG in the material decreases monotonically with pressure below 12 GPa, and does not depend on pressure above 12 GPa. The results provide no-evidence for high pressure ferroelectricity in PbTiO$_{3}$ at high pressure and room temperature.