Key Engineering Materials Vol. 566

Abstract: The a-axis oriented ZnO thin films deposited on sapphire substrates by pulsed laser deposition were studied to investigate the effects of pre-annealing on oxygen diffusion. The effect was as follows: the oxygen diffusion coefficient decreased, and the oxygen concentration in the tailing regions of the profiles reduced. Ion images of an oxygen tracer revealed the high-diffusivity paths for oxygen tracer diffusion. The temperature dependence of oxygen tracer diffusion coefficients (D_b) in as-deposited and pre-annealed thin films were determined to be D_b [cm²/ = 9.2x10² exp (- 405 [kJ/mo / RT) and D_b [cm²/ = 1.8x10³ exp (- 418 [kJ/mo / RT), respectively. On basis of these results, the crystal orientation on D_b and the mechanism for oxygen diffusion were discussed.

Abstract: Highly dispersed barium titanate (BaTiO₃, BT) nanoparticles were prepared by the new 2-step thermal decomposition method of barium titanyl oxalate of 30 nm in size. The nanoparticles were heated at 450 °C for 5 hours in air to yield intermediate product: Ba₂Ti₂O₅CO₃. Highly dispersed BaTiO₃ nanoparticles were prepared by rotationally stirring it at the reduced pressure of 0.2 Pa at various temperatures between 800 °C and 900 °C. The particle size and morphology of the BaTiO₃ nanoparticles were investigated by X-ray diffraction and scanning electron microscopy. These measurements showed that the BT nanoparticles were highly dispersed and well-crystallized.

Abstract: Highly crystallized BaTiO₃ thin films were fabricated by a nanocrystal sintering process. Boron alkoxide was introduced into a slurry of Mn-doped BaTiO₃ nanocrystals with particle sizes of 5-7 nm. The deposited nanocrystal film on a (111)-oriented Pt/TiO₂/Al₂O₃ substrate was sintered at a low temperature of 800 °C and the obtained film had highly densified and oriented microstructures. We found that the boron additive enhanced the grain growth of nanoparticles and as a result the dielectric constant of the thin film increased to 1100 at 10 kHz, which is much higher than that of undoped BaTiO₃ thin films.

Abstract: BaTiO₃ nanopowders were prepared by salt-assisted spray pyrolysis using a flux of KNO₃ and NaNO₃. Compounds of metal sources are thermally decomposed in the melting flux. Some flux mixtures make a eutectic composition because of the reduced melting point of the flux. The optimum temperature for the preparation of BaTiO₃ nanoparticles was 700 °C. When both KNO₃ and NaNO₃ were used as the flux, the average particle size of the BaTiO₃ powders was 40 nm, and the particle distribution was broad. On the other hand, when only KNO₃ was used, the average size of BaTiO₃ powders was 60 nm, and the particle distribution was narrow. This suggested that the sodium ions in the BaTiO₃ nanoparticles led to a broad particle distribution. X-ray diffraction (XRD) revealed that all the diffraction peaks were in agreement with the crystal phase of BaTiO₃. The relative density of the sintered body of BaTiO₃ powders was 87 %. The relative dielectric constant of the sintered body was 1180, and the dielectric loss (tanδ) was 0.023 at room temperature. This suggested that the residual potassium ions in the BaTiO₃ nanoparticles led to a reduction in the relative density and dielectric constant.

Abstract: Barium titanate (BT) and strontium titanate (ST) nanocubes which have been synthesized by hydrothermal method with surfactants were assembled in order directly on the substrates by using capillary-force-assisted self-assembly method. The ordered structures, crystallinity and orientation of the nanocubes were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning probe microscopy (SPM) and X-ray diffraction (XRD). The piezoresponse properties of the nanocubes ordering structures characterized by Piezoresponse Force Microscopy (PFM) seemed to depend on the constituents and their interface.

Abstract: Solvothermally synthesized strontium titanate (SrTiO₃, ST) or barium titanate (BaTiO₃, BT) nanocubes were accumulated and the dielectric properties were studied. Initially, the BT or ST nanocubes were pressed into pellets. BT was deposited on the pellets by a solvothermal method. P-E hysteresis loops and S-E curves of BT-coated ST accumulation ceramics (BT on ST) showed ferroelectric responses. The dielectric constant of the accumulation ceramics was measured to be 70.6.

Abstract: The strontium titanate (SrTiO₃, ST) -coated barium titanate (BaTiO₃, BT) complex nanoparticles was prepared. Using this condition, ST-coated BT (ST/BT) and ST-coated ST (ST/ST) nanocube accumulation ceramics were successfully prepared with epitaxial interface between ST and BT. Dielectric properties were measured for the both accumulation ceramics, but there was no difference of the dielectric properties between both ceramics, and the origin of the result was discussed.

Abstract: In this study, strontium titanate (SrTiO₃, ST) nanocube particles were successfully prepared, with a size of 12 nm, normal size distribution with standard deviation of 10 %, and sharp edge corner, by solvothermal method using complex titanium raw materials of TiO₂ and titanium isoproxide. Moreover, the well-dispersed ST nanocube slurry was also prepared using electric double layer with hydrochloric acid. Finally, using the ST nanocube slurry, ST nanocube accumulation was prepared by two kinds of forces of capillary force and absorption force by plaster. The obtained ST nanocube accumulation was not 3-dimentional aliened ST nanocube structure, but randomly piled structure.

Abstract: Calcium phosphate powders (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, and tetracalcium phosphate) were electrically polarized by an applied dc voltage. Thermally stimulated depolarization current measurements confirmed that each calcium phosphate powder exhibited surface charges after polarization treatment. The surface adsorption of simvastatin on each powder was investigated. We observed a difference in adsorption between polarized and non-polarized powders. This difference in adsorption is due to the electrostatic force between the polarized surface and the open-ring form of simvastatin, which has a larger electrical polarity than its closed-ring form.

Abstract: We prepared a niobiophosphate-glass-crystallizing tungstenbronze-type Ba₂NaNb₅O₁₅ and measured elastic light scattering spectra in situ in the glass-ceramics fabrication regime. We found that the studied glass possesses a strong tendency for phase separation into Al₂O₃P₂O₅ and Nb-rich regions prior to crystallization. It is suggested that the tungstenbronze phase crystallizes in the Nb-rich region separated from the supercooled liquid phase. This study demonstrated that in situ Raman spectroscopy is also useful for observing the phase separation dynamics in glass.