Papers by Author: Satoshi Wada

Abstract: Barium zirconate (BaZrO₃) was prepared by the composite-hydroxide-mediated (CHM) approach at low temperature. The CHM method is based on chemical reactions of materials in the eutectic hydroxide melt. In this method, the eutectic point at an sodium hydroxide (NaOH) : potassium hydroxide (KOH) molar ratio of 51.5 : 48.5 is about 165°C. In the present work, the low-temperature preparation and morphology of BaZrO₃ nanocrystals were investigated. Zirconium tetra-n-butoxide ((CH₃CH₂CH₂CH₂O)₄Zr) and/or zirconium dioxide (ZrO₂) were used as a zirconium source. X-ray diffraction measurements confirmed that the BaZrO₃ had a perovskite structure. Barium hydroxide (Ba (OH)₂) was used as a barium source. BaZrO₃ nanoparticles were obtained when (CH₃CH₂CH₂CH₂O)₄Zr was used as a raw material. On the other hand, BaZrO₃ nanocubes were formed when ZrO₂ was used as a raw material. Scanning electron microscopy and transmission electron microscopy observations indicated that BaZrO₃ nanocrystals were formed.

Abstract: The barium titanate (BaTiO₃, BT) epitaxially coated strontium titanate (SrTiO₃, ST) (BT/ST) nanocube accumulation ceramics were successfully prepared by a sorbothermal method, with epitaxial interface between ST and BT, and as reference, the BT/BT nanocube accumulation ceramics were also preapred. These dielectric properties were measured for the both accumulation ceramics, and it was clearly obserbed that there was significiant difference between BT/ST and BT/BT nanocube accumulation ceramics in the dielectric properties under low and high electric fields, and the origin of the result was discussed.

Abstract: Porous barium titanate (BaTiO₃, BT) ceramics were prepared by a conventional sintering method using two kinds of BT particles. The relationship between pore structure (porosity and pore size) of BT ceramics and their sensor properties was investigated. Since a piezoelectric d₃₃ constant of BT depends largely on the pore structures, the microstructure control of porous BT ceramics is important to improve the figure-of-merit (g₃₃/ρ). In this study, the maximal piezoelectric g₃₃ constant value of 14.8×10^-3 V·m·N^-1 and the maximal g₃₃/ρ value of 3.14×10³ V·m⁴·N^-1·g^-1 were recorded at a porosity of approximately 23%.

Abstract: Barium titanate (BaTiO₃, BT) grain-oriented ceramics were prepared by electrophoresis deposition (EPD) method under high magnetic field (HM-EPD) of 12 T. For this objective, the BT single-domain nanoparticles with high c/a ratio of 1.008 and size of 103 nm were prepared by two-step thermal decomposition method. Using the BT nanoparticle slurry, BT nanoparticle accumulations were prepared by EPD or slipcasting (SC) methods with/without high magnetic field. After binder burnout, these accumulations were sintered at 1350 °C and it was revealed that only the BT ceramics prepared by the HM-EPD method was assigned to grain-oriented ceramics with weak preferential crystallographic orientation along [11 direction.

Abstract: Barium titanate (BaTiO₃) nanoparticles were prepared by a 2-step thermal decomposition method using nanooxalate particles. BaTiO₃ nanoparticles were characterized using various methods. Accumulations were prepared by electrophoresis deposition method using the obtained BaTiO₃ nanoparticles. They were performed necking structure by a solvothermal method. Polymer was infiltrated into the accumulations in vacuum to prepare a polymer film capacitor.

Abstract: Lead-free (Bi_0.5K_0.5)TiO₃)-Bi (Mg_0.5Ti_0.5)O₃-BiFeO₃ (BT-BMT-BF) ceramics were prepared by a conventional solidstate synthesis. Synchrotron x-ray diffraction studies indicated two compositional phase boundaries. An increased strain of 0.070% was obtained at 50 kV/cm, 1 Hz, 25 °C for one of the phase boundary compositions of 0.45BKT-0.1BMT-0.45BF with the temperature of the dielectric maximum of 331 °C.

Abstract: Bismuth potassium titanate ((Bi_1/2K_1/2)TiO₃: BKT) powder were prepared using bismuth oxide (Bi₂O₃), potassium hydrogen carbonate (KHCO₃) and titanium oxide (TiO₂) raw materials. Barium titanate (BaTiO₃: BT) platelike particles oriented along [110] direction were used as template particles. Barium titanate-bismuth potassium titanate (BT-BKT) ceramics had a tetragonal phase at -100 °C. The main composition was fixed to BKT 30 molar% because the Curie temperature (T_C) was well above 200 °C at BKT 30 molar%. The orientation of [110]-oriented BT-BKT ceramics (BKT 30 molar%) was 54.6 %.

Abstract: 1-x-y)BaTiO₃-xBi (Mg_1/2Ti_1/2)O₃-yBiFeO₃ ceramics were prepared by a conventional solidstate synthesis, and crystal structure and electric properties were investigated. Synchrotron X-ray diffraction pattern revealed that a single perovskite phase was obtained for samples at x=0.05-0.15, y=0.46.5-73.5. Splitting of the (111) peak was observed when (x, y) = (0.050, 0.685) and (0.050, 0.735) indicating that crystal structure of samples changed from a pseudo-cubic phase to a rhombohedral phase with increasing BF. As the BF content increased, the Curie temperature increased. The largest maximum strain (S_max) over the applied maximum electric field (E_max) value (S_max / E_max) of 300 pm/V was observed for 0.365BT-0.050BMT-0.585BF at 25 °C and 1Hz with the Curie temperature of 390 °C.

Abstract: Denser, solvothermally synthesized KNbO₃ (KN) / BaTiO₃ (BT) composites with heteroepitaxial interfaces were prepared using the barium titanate powder with a wide particle size distribution. The relative density was 68 - 80 %, which was larger than that of the composites prepared using the barium titanate powder with a narrow particle size distribution. The dielectric constant was 300 450 and it was maximized at the KN/BT molar ratio of 0.5. The origin was discussed with the microstructure and crystal structure.

Abstract: Bismuth and niobium based perovskite oxides with non-integer A and B site valences were prepared by a solid-state route. For the A^1+xB^5xO₃ type (Bi_x/2K_1-x/2)(Ti_xNb_1-x)O₃ (x=0.1 0.9) ceramics (the examples of samples studied), the Curie temperature increased from approximately 250 to 350 °C with increasing x from 0.5 to 0.9. These results were discussed with the Abrahams relations.