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-xLa_xTi_1-3/4xO₃(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.