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Size Dependence of Dielectric Properties for nm-sized Barium Titanate Crystallites and Its Origin
S. Wada,H. Yasuno,H. Kakemoto,M. Yashima,S.-M. Nam,T. Tsurumi,T. Hoshina 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Barium titanate (BaTiO3) crystallites with various particle sizes from 17 to 1,000 nm were prepared by the modiffed 2-step thermal decomposition method. Investigation of impurities in these particles by using both TG-DTA and FT-IR measurements revealed that no impurity was detected in the BaTiO3 lattice, while hydroxyl and carbonate groups were detected only on the surface. Moreover, their relative densities were always above 99 %.The dielectric constants of these powders were measured by using slurries by a modied powder dielectric-measurement method. As a result, the dielectric constant of BaTiO3 particles with a size of around 140 nm exhibited a maximum of around 5,000. By using a synchrotron-radiation X-ray powder experiment, the crystal structure of the BaTiO3 particles with sizes below 100 nm was investigated. As a result, in the BaTiO3 particles with sizes over 40 nm, it was conrmed that their crystal structure was assigned to 4 mm. In the particle size with a maximum dielectric constant of 5,000, its c=a ratio was smaller than 1.011. Finally, to explain the origin of the high dielectric constant, a model related to \superparaelectric behavior" was proposed.
Origin of Ultrahigh Dielectric Constants for Barium Titanate Nanoparticles
Satoshi Wada,C Moriyoshi,H. Yasuno,K Kakemoto,K Takizawa,M Ohishi,T Hoshina,T Tsurumi,Y Kuroiwa 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Barium titanate (BaTiO3) nanoparticles with various particle sizes from 17 to 1,000 nm were prepared by using the 2-step thermal decomposition method of barium titanyl oxalate under various degree of vacuum. Various characterizations revealed that these particles were impurity-free, defectfree, dense BaTiO3 nanoparticles. When the degree of vacuum was high (pressure of 150 Pa at 650 C), the dielectric constant of BaTiO3 particles with a size of around 60 nm exhibited a maximum of around 15,000. On the other hand, when the degree of vacuum was low (pressure of 400 Pa at 650 C), no dielectric maximum was observed. To explain this size dependence, we precisely investigated a particle structure by using synchrotron radiation. As a result, the particles were always composed of two layers, i.e., a surface cubic layer and a bulk tetragonal layer, and the thickness of the surface cubic layer decreased with increasing degree of vacuum during the preparation of BaTiO3 nanoparticles. Thus, we confirmed that the surface structure was an important factor in determining the dielectric properties of BaTiO3 nanoparticles.