钛酸铅超微粉的铁电相变与颗粒尺寸的关系

报道了钛酸铅超微粉的粉粒尺寸对其铁电相变的影响，所用超微粉是用溶胶－凝胶法制备的，尺寸在２０ｎｍ至２００ｎｍ之间。在常温用Ｒａｍａｎ散射测量了软模频率，发现软模频率随尺寸减小而降低。用Ｘ射线衍射测量了晶轴比ｃ／ａ，小尺寸超微粉的ｃ／ａ较接近于１。根据比热反常确定了相变温度，发现随着尺寸减小相变温度降低，而且相变的弥散性增加。相变温度Ｔｃ与粒子尺寸Ｄ的关系可用经验公式Ｔｃ（Ｄ）＝７６６－２５６／（Ｄ

SIZE DEPENDENCE ON FERROELECTRIC PHASE TRANSITION IN PbTiO_3 ULTRAFINE PARTICLES

Effect of particle size on ferroelectric phase transition in PbTiO_3 ultrafine particles is reported.Theultrafine particles used were prepared by sol-gel process,with the size ranging from 20nm to 200nm. The softmode frequency was measured at room temperature by Raman scattering,which is found to decrease with theparticles size,The axis ratio c/a was measured by X-ray diffraction,The smaller the size,the nearer the c/ato unity 1.The phase transition temperature was determined,based on specific heat anomaly. With the decreaseof size,the phase transition temperature decreases and the diffuseness of the transition increases. The dependenceof phase transition temperature T_c on the particle size D(in nm)can be expressed by the ernpirical formula :T_c(D)=766-256/(D-8.8)(K),where 766K is the transition temperature for bulk PbTiO_3 and 9. 1nm isthe critical size below which ferroelectricity disappears.