No abstract

In this study, the particle dispersion state in a dense BaTiO 3 slurry containing a dispersant and binder was assessed by various slurry evaluations such as particle size distribution measurement by laser diffraction, viscosity measurement, dynamic viscoelasticity measurement, and hydrostatic pressure measurement, which is a novel slurry evaluation technique developed by our group. Then, the relationship between the slurry evaluation results and the packing fraction of green sheets fabricated from these slurries was discussed. We found that the particle size distribution and the relative viscosity and yield stress by dynamic viscoelasticity measurement could not properly estimate the packing fraction of green sheets. In contrast, the hydrostatic pressure measurement was able to distinguish the particle dispersion state, and the results show an acceptable correlation with the packing fraction. The reason is that our developed method evaluates not only the initial particle dispersion state, but also its change as the particle concentration increases. ARTICLE HISTORY

No abstract

Group-III nitride alloys are currently used in various microwave communication applications because of the giant enhancement in electromechanical coupling after alloying with rocksalt nitrides such as YbN or ScN. Herein, the Yb-substitution-induced enhancement for electromechanical coupling in wurtzite III−V nitrides is studied via theoretical calculations and experiments. The substitution-induced mechanical softening and local strain can enhance electromechanical coupling. The mechanical softening shows less dependence on the parent AlN or GaN, which is considered to be caused by the Yb−Yb pair interaction in the c-axis, and the difference of electromechanical coupling between the GaN-and AlNbased alloys mainly comes from the enhancement effect of Yb substitution for the piezoelectric response. The largest change in the piezoelectric response relative to the parent nitride is observed in the GaNbased alloy, and is mainly attributed to a small piezoelectric constant of the parent GaN, which makes GaN as the parent nitride difficult to improve its electromechanical coupling coefficient compared with AlN-based alloys. Moreover, our calculations reveal that the substitutional element with a closer ionic size to the host cation is easier to substitute into the host nitride and produces a larger internal strain to partly contribute to the enhancement in the piezoelectric response. This can serve as a simple guideline to identify alloying components in a search for a massive increase in electromechanical coupling.

Suspension spraying is a promising surface modification technique, because finer particles can be used in contrast to the case of conventional thermal spraying. However, the optimal conditions for preparing suitable suspensions have not yet been established. Thus, the effects of particle dispersion and flocculation states on the properties of suspension-sprayed coatings were examined in the present study. Y 2 O 3 suspensions were prepared using various quantities of the dispersant. The flow curves and gravitational settling behaviors of the prepared suspensions were investigated. The amounts of the dispersant adsorbed on the particles were also determined. In addition, Y 2 O 3 coatings were fabricated using suspension spraying, and the properties of the obtained coatings were investigated. The addition of the dispersant affected the suspension flow characteristics, because the amount of the dispersant adsorbed increased with increasing dispersant concentration. Furthermore, the coating characteristics improved as the apparent viscosity of the suspension decreased.