Hiroaki Yasuno

Preparation of nm-Sized Barium Titanate Fine Particles and Their Powder Dielectric Properties

Barium titanate (BaTiO3) crystallites with various particle sizes from 17 to 100 nm were prepared by the 2-step thermal decomposition method of barium titanyl oxalate (BaTiO(C2O4)24H2O). The crystal structure of these BaTiO3 particles was assigned to cubic m-3m by a X-ray diffraction (XRD) measurement while it was assigned to tetragonal 4mm by a Raman scattering measurement. Investigation of impurity in these particles 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. The dielectric constants of these powders were measured using suspensions by a modified powder dielectric measurement method. As a result, the dielectric constant of BaTiO3 particles with a size of around 70 nm exhibited a maximum of over 15,000. This study revealed that BaTiO3 particles with a size around 70 nm were the most desirable for capacitor application.

Preparation of nm-Sized BaTiO3 Crystallites by The 2-Step Thermal Decomposition of Barium Titanyl Oxalate and their Dielectric Properties

In this study, we proposed to prepare the fine BaTiO 3 particles by a new 2 step decomposition of barium titanyl oxalate (BaTiO(C2O4)2•4H2O). The 1st step is the thermal treatment of BaTiO(C 2 4)2•4H2O at 400 ̊C for 1 hour under O 2 flow for the purpose of the removal of carbon species. The 2nd ste p is the formation of the fine BaTiO3 particles by the thermal treatment at various temperatures in vacuum. As a typical case, the fine BaTiO 3 particles with a size of about 16.5 nm were obtained by the treatm ent at 600 ̊C for 0.5 hour in vacuum. The dielectric properties of these parti cles were measured below 30MHz using the impedance analyzer. This method was composed of tw o parts; (1) the dielectric measurement using the slurry of the BaTiO 3 crystallites with 1-propanol and (2) the simulation using the electrostatic field analysis of the finite element method. When t se two kinds of the values become to same, the dielectric constant of the BaTiO 3 crystallites can be determined. Using this powder dielectric measurement, the dielectric constant of the BaTiO 3 crystallites with a size of 16.5 nm was determined at almost 400.

Particle Size and Temperature Dependence of THz-Region Dielectric Properties for BaTiO3 Nanoparticles

Impurity-free, defect-free and dense barium titanate (BaTiO 3 ) nanoparticles with various particle sizes from 22 to 500 nm were prepared using a 2-step thermal decomposition method. Powder dielectric measurement clarified that dielectric constant of BaTiO 3 particles with 58 nm exhibited a maximum around 15,000 at 20.00°C. To explain this high dielectric constant, THz-region dielectric properties of BaTiO 3 nanoparticles, especially Slater transverse optic (TO) mode frequency, were estimated using the far infrared (FIR) reflection method. As the result, it was found that the Slater TO mode of BaTiO 3 particles with 58 nm exhibited a minimum.

Size Effect of Dielectric Properties for Barium Titanate Particles and Its Model

Powder dielectric measurement of barium titanate (BaTiO3) fine particles from 17 to 1,000 nm revealed a maximum dielectric constant at a certain particle size. The sizes with maximum dielectric constants were strongly dependent on preparation methods. When BaTiO3 fine particles were prepared in vacuum of 10-2 torr, a dielectric maximum of 15,000 was observed at 70 nm. On the other hand, when BaTiO3 fine particles were prepared in air, a dielectric maximum of 5,000 was observed at 140 nm. Structure refinement of BaTiO3 particles using a Rietveld method revealed that all of BaTiO3 particles were composed of two parts; (a) surface cubic layer and (b) bulk tetragonal layer. Moreover, a thickness of surface cubic layer for BaTiO3 particles prepared in vacuum was much thinner than that for BaTiO3 particles prepared in air. To explain the differences, a new model on the basis of “surface relaxation” was proposed.

Evaluation of Dielectric Permittivity of Barium Titanate Fine Powders

Dielectric permittivity (e r ) of BaTiO 3 (BTO) powders was determined by measuring e r of slurries prepared from BTO powder and propylene carbonate as dispersion medium, followed by analyzing with a finite element methods (FEM). The e r of powders depended on their characters such as tetragonality ( c / a ratio), density, particle size and specific surface area. In order to extract the effect of each character, a statistical analysis was carried out to represent the e r of powders with an empirical formula, where the c / a ratio, density and particle size were used as parameters. A fairly good agreement between observed data and those expected from the formula was obtained and the contribution of each character to the e r could be determined.

Dielectric Measurement of BaTiO3 Powder and Its Statistical Analysis

Dielectric permittivity of BaTiO3 powders was determined by measuring permittivity of slurries prepared from BaTiO3 powder and propylene carbonate as dispersion medium followed by analyzing with a finite element methods (FEM). The permittivity of powders depended on their characters such as tetragonality (c/a ratio), density, particle size and specific surface area. In order to extract the effect of each character, a statistical analysis was carried out to represent the permittivity of powders with an empirical equation where the c/a ratio, density and particle size were used as parameters. A fairly good agreement between observed data and those estimated from the relation was obtained and the contribution of each character to the permittivity could be determined.