Abstract: 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.

Key words: BaTiO₃, Size effects, XRD, Phase transition