The effects of grain size on the ferroelectric transition temperature in na
no-crystalline complex ferroelectric perovskite oxides, have been investiga
ted employing micro-Raman scattering spectroscopy as a function of temperat
ure and pressure. There appears a distinct soft mode induced phase transiti
on in each sample and the transition temperature decreases with decreasing
grain size. For example, the observed soft mode Raman frequency in pure PbT
iO3, with grain size of 60 nm, remarkably shifts to lower frequency relativ
e to single-crystal, powder or thin film data, clearly indicating a lowerin
g in its transition temperature. Grain size-induced phase transformation fr
om ferroelectric tetragonal to paraelectric cubic phase in nano-crystalline
Pb1-xBaxTiO3, is found to occur at x=0.7 and it is associated with the Ba
concentration dependence of the soft mode. These studies show possibility o
f preparing high efficiency PbTiO3 sensors that can be operated close to am
bient temperature.