PHASE-TRANSITION IN PBTIO3 ULTRAFINE PARTICLES OF DIFFERENT SIZES

The size effect on the ferroelectric phase transition in PbTiO3 ultra-fine particles is reported. Samples with particle sizes from 20 to 200 nm were prepared by a sol-gel process followed by calcining at different temperatures. The particle size was determined by x-ray diffraction from the integrated width of diffractions. The soft-mode frequency at room temperature was measured by Raman scattering. It decreases with decreasing particle size. The ferroelectric phase transition was traced by specific-heat measurement. The transition temperature decreases and the transition becomes diffused as the particle size decreases. The size dependence of T(C) can be described by T(C)(D) = 766 - 256/(D - 8.8) (K), where 766 K is the T(C) for bulk PbTiO3 and D (nm) is the particle size. This equation gives a critical size of 9.1 nm below which ferroelectricity disappears.Physics, Condensed MatterSCI(E)171ARTICLE162619-2624