纳米晶钛酸钡的Sol-gel法制备及其尺寸效应

Preparation of Nanometer-sized BaT iO_3 Crystallites by Sol-gel Method and Size Effects on Structure 

采用sol-gel法制备了不同粒径的钛酸钡(BT)纳米晶粉.XRD、Raman光谱和DSC测试结果显示,随着退火温度的升高,晶粒长大,晶胞的a轴逐渐减小,c轴逐渐增大.粒径在54nm左右时,钛酸钡由顺电立方相向铁电四方相结构转变,在立方-四方相变过程中,晶胞略微膨胀.随着粒径的减小,正交-四方相变温度升高,四方-立方相变温度降低,Raman谱峰降低和宽化,粒径为38nm左右时四方相的特征峰消失.

Nanometer-sized BaTiO 3 crystallites in different sizes hav e been prepared by sol-gel method.The crystal structure,phase transitio n and Raman spectra of the BaTiO 3 crystallites were investigated by X RD,Raman spectra and DSC.The results in dicated that BaTiO 3 crystallite forms at temperature of 750℃.The average grain size is about 38nm and t he crystal structure belongs to the c ubic paraelectric phase.With the increase of annealing temperature,the grain becomes larger and a axis becomes shorter while c axis becomes longer gradually.The crystal structure begins to change to the cubic paraelectric phase from the tetragonal phase at about 54nm of average grain .The crystal structure of BaTiO 3 crystallite with an average grain size of about 102nm belongs to tetragonal phase.During the decrease of average grain s ize,the temperature of phase tran-sition from orthodoxy to tetragonal increases while the temperature of p hase transition from tetragonal to c ubic decreases.There exists a heat stagn ation in phase transition and the heat stagnation decreases gradually wi th the decreasing grain size.The frequencies of Raman bands strongly depend on grain sizes and structures of the BaTiO 3 crystallite.The characteristic peaks of tetragonal phase disappear at about 38nm of average grain.