纳米晶钛酸钡的Sol-gel法制备及其尺寸效应

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54 nm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38 nm左右时四方相的特征峰消失.

Preparation of Nanometer- sized BaTiO3 Crystallites by Sol- gel Method and Size Effects on Structure

Nanometer-sized BaTiO3 crystallites in different sizes have been prepared by sol-gel method. The crystal structure, phase transition and Raman spectra of the BaTiO3 crystallites were investigated by XRD, Raman spectra and DSC. The results indicated that BaTiO3 crystallite forms at temperature of 750 ℃. The average grain size is about 38 nm and the crystal structure belongs to the cubic 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 54 nm of average grain. The crystal structure of BaTiO3 crystallite with an average grain size of about 102 nm belongs to tetragonal phase. During the decrease of average grain size, the temperature of phase transition from orthodoxy to tetragonal increases while the temperature of phase transition from tetragonal to cubic decreases. There exists heat stagnation in phase transition and the heat stagnation decreases gradually with the decreasing grain size. The frequencies of Raman bands strongly depend on grain sizes and structures of the BaTiO3 crystallite. The characteristic peaks of tetragonal phase disappear at about 38 nm of average grain.