Key Engineering Materials Vol. 301

Abstract: A new method for ultrafine barium titanate (BaTiO3) particles with diameters of around 5 nm is proposed. In this method, barium titanyl oxalate aqua solution with low concentration below 10-3 mol/l was used as the starting material. The droplets with a size below 3 μm were atomized with an ultrasonic vibrator, dried and thermally decomposed at higher temperatures over 300°C. In the preparation of the BaTiO3 particles, there were two parameters such as thermal decomposition temperature and precursor solution concentration. Therefore, various particles were prepared by changing these parameters. Finally, non-aggregated nm-sized BaTiO3 particles with an average diameter of 5.2 nm, despite wide size distribution from 2 to 20 nm, were prepared by using the precursor solution with 10-6 mol/l.

Abstract: Barium titanate (BaTiO3) nano-particles with high crystalinity were synthesized by hydrothermal process using Ba(OH)2·8H2O and TiO2 as source materials. The average size of the synthesized BaTiO3 particles decreased as the TiO2 particle size decreased. The amount of hydroxide ions incorporated into the perovskite lattice decreased as the BaTiO3 particle size increased and then became constant above 50 nm. Moreover, the ratio of the c- to a-axis length increased when the BaTiO3 particle size was above 50 nm. Sintered ceramics with a grain size smaller than 100 nm were obtained by using highly crystallized hydrothermal BaTiO3 particles.

Abstract: BaNd2Ti4O12 dielectric oxide particles were spheroidized by melting them with a LPG-O2 flame to improve packing and fluidity of the powder. Changes in the particle morphology, structure and crystallinity during the process were investigated. It is revealed that most of the as-melted particles are dense, spherical and amorphous with smooth surfaces, which crystallize in the annealing process to form polycrystalline spherical particles with uneven surfaces. Annealing at above 1100°C is necessary for the spheroidized powder to recover its crystallinity and dielectric properties.

Abstract: We present a new method for soft chemical synthesis of perovskite materials. Perovskite K1-xLixNbO3 powders are produced by an ion-exchange reaction of layered perovskite precursor, K2NbO3F, with lithium chloride in water at room temperature. X-ray diffraction and X-ray fluorescent spectroscopic studies show that a mechanism of the ion-exchange reaction is a self-assembly between the perovskite nanosheets in aqueous solution.

Abstract: Compositionally uniform nitride powders were synthesized from metal oxide powders using a fluidized bed in NH3 or NH3-N2 flows. GaN was synthesized by a two-step heating ; the first step was done at 700°C for 1 h; the second step was done at 900°C for 4 h. GaN-ZnO solid solution was synthesized at 900°C for 4 h. The grain sizes of the products were smaller than those of the starting materials.

Abstract: Fine powder of CaZrO3 (CZ) was synthesized by using ultra-fine and highly dispersed CaCO3 as a precursor. The results showed that the calcination temperature could be reduced to inhibit grain growth of CZ. Mean grain size of the CZ fine powder was 80 nm. Moreover, the CZ powder was used to synthesize a solid solution of (Ba,Ca)(Zr,Ti)O3 (BCZT) to examine the effect of the powder’s grain size on the reactivity of BT and CZ. It was found that the fine CZ powder enhanced the BT and CZ reaction.

Abstract: The crystal structures of barium titanate (BaTiO3) fine particles with a size around 140 nm were investigated using a synchrotron radiation X-ray diffraction method. The observed diffraction pattern was analyzed by Rietveld method assuming several models. As a result, it is found that the BaTiO3 fine particles have composite structures include (a) a tetragonal region with a constant c/a ratio, (b) a tetragonal region with gradient c/a ratios and (c) a cubic region. In order to estimate these structures, the partial profile relaxation technique was applied in the Rietveld refinement. It is considered that the composite structure is important for the size effect on BaTiO3 fine particles.

Abstract: Micrometer wire consisting of microbeads was successfully fabricated onto a patterned conductive electrode substrate by an electrophoretic deposition (EPD) process with precise control of electric field distribution generated in the colloidal suspension. Monodisperse polystyrene microspheres with 320 nm in diameter and an interdigitated microarray Au electrode having 10 μm in width and 5 μm in spacing were used in this EPD system. A micropattern of polystyrene particles with two dimensional arrays was formed onto the patterned electrode by the EPD process with two electrode system using an electrostatic interaction between the electrodes and the charged particles in the suspension.

Abstract: Electron beam lithography combined with electrophoretic deposition was investigated to fabricate micropatterned barium titanate (BTO) with nanostructures. High quality resist molds with micropatterns of microgrids and microdot arrays were prepared on Pt/Ti/SiO2/Si substrate by electron beam lithography. BTO nanocrystallites in a pseudo-cubic perovskite phase with an average particle size of about 10 nm were synthesized by a high-concentration sol-gel process. Well-dispersed and stable suspensions of barium titanate nanocrystallites were synthesized. Then, BTO microlines, microgrids and microdot arrays were electrophoretically deposited on micropatterned Pt/Ti/SiO2/Si substrate from these suspensions. The microstructure and properties of the BTO micropatterns were evaluated.

Abstract: 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.