Size-induced phase transition in PhTiO3 nanocrystals:: Raman scattering study

We report a Raman scattering study of PbTiO3 (PT) nanocrystals prepared by a sol-gel method at a low temperature of 400 degrees C. The Raman spectra indicated the existence of a stable ferroelectric phase in the PT nanocrystals at room temperature. The temperature dependence of the spectrum revealed the appearance of a new phase transition in the 7-nm PT nanocrystals in the region of 166 degrees C. This was attributed to the phase transition between C-4v and C-2v point groups induced by the size reduction of the PT crystals to nanoscale. This feature is significantly different from that observed for conventional PT materials in which only the tetragonal phase is detectable below 493 degrees C.