Size Effects on the Crystallite Structure and Phase Transition in Lanthanaum-Modified Lead Titanate Nanocrystals

The size effects on the crystallite structure,Raman spectra as well as phase tian-sition in lanthanum-modified lead titanate Pb_(1-x)La_(x)Ti_(1-3/4x)O_(3)(x=0.14)(PLT14)nanocrystalline powders were investigated.The results show that with decreasing grain size,the crystallite structure changes from tetragonal perovskite phase to cubic perovskite phase;the soft mode frequency at room temperature decreases,and disappears when the grain size is as small as 19nm;the phase transition temperature from ferroelectric to paraelectric shifts towards a low temperature region.The phase transition in nanocrystalline PLT14 is a second order one,which is confirmed by its dielectric constant measurement.