Muneyasu Suzuki

Temperature-dependent structural variations of ceramic coatings of lead titanate PbTiO₃ (PT) formed at room temperature (RT) via aerosol deposition (AD) have been investigated to evaluate the stability of the ferroelectric phase. Synchrotron radiation x-ray diffraction experiments in the as-deposited state showed a polycrystalline film oriented preferentially along the c-axis of the perovskite-type ferroelectric tetragonal structure on the quartz glass substrate. The c-axis orientation may be attributed to the anisotropic structural characteristics of the crystal with a layered structure composed of a two-dimensional (2D) covalent bonding network in the ferroelectric phase at RT. The 2D interfaces of the ceramic particles in the aerosol, which are chemically activated by collision with the substrate, are most likely to recombine during the AD process and form a dense and hard coating at RT. When the PT film was heated to the paraelectric phase with a cubic structure at 1000 K, the c-axis orientation observed in the as-deposited state disappeared upon cooling owing to the degree of freedom in selecting the polar axis associated with the cubic-tetragonal phase transition. The spontaneous lattice distortion of the AD film at RT was smaller than that of the bulk ceramic. However, the phase transition temperature (T_C) was approximately 100 K higher only during the first heating process from the c-oriented as-deposited state. The AD method stabilizes the ferroelectric phase up to a higher temperature, although the spontaneous polarization is suppressed. The ferroelectric ceramic materials synthesized mainly via particle collisions are assumed to have low ferroelectricity but high T_C.

Flexible or stretchable devices have been attracting attention because of the increase in popularity of internet-of-things devices and wearables. Because lithium-ion secondary batteries have rigid bulk shapes and therefore affect bodily motion, their use in such devices is problematic. Demand for plantar pressure-measuring devices has increased because impairment of ambulation leads not only to accidental falls by elderly people but also to arthritic disorders such as backaches induced by hallux valgus, calluses, and ingrown nails. Because the design of such a small, lightweight device with a medium-capacity lithium-ion battery is impossible, the collection of sufficient data has been impossible. We designed a novel all-solid-state battery produced with a solid-state electrolyte. The battery discharged even when folded, cut, or pushed. This 440 mAh battery could be used to improve overall usability of a prototype of an insole device that would consist of pressure sensors, a wireless communication device, and the battery.

The validity of the mechanochemical solid-state reaction by dry ball milling for synthesizing Pb(Zr, Ti)O ₃ (PZT) fine ceramic powder at room temperature (RT) was evaluated using synchrotron radiation X-ray diffraction (SXRD). A mixture of PbZrO ₃ (PZ) and PbTiO ₃ (PT) powders with a molar ratio of 1:1 was prepared as the starting powder. To confirm the synthesis of PZT, the structural characteristics of the ball-milled samples with different milling times were investigated by analyzing the SXRD data using the Rietveld method. The solid-state reaction was nearly complete in a short milling time of 4 h at RT. After ball milling for approximately 8 h, only a single phase of PZT was detected. The Rietveld refinement for the crystal structure analysis demonstrated that slightly Ti-rich PZT, Pb(Zr _0.485(1) Ti _0.515(1) )O ₃ , with a tetragonal crystal system, is synthesized in the 8 h sample. The tetragonality is sufficiently suppressed to resemble a cubic system even at RT, whereas the phase transition temperature ( T _C ) is significantly high. We quantitatively demonstrate that PZT with a higher T _C can be synthesized at RT by dry ball milling, despite the smaller spontaneous lattice distortion.

Recently, the demand for flexible or stretchable Internet‐of‐things devices has increased with the rise in popularity of wearables. Also, research is progressing for the development of oxide‐based all‐solid‐state lithium‐ion batteries, which are expected to have improved safety and performance compared with current batteries. Room‐temperature processes for the production of oxide films would facilitate the development of such novel devices. Press forming is a simple room‐temperature process; however, conventional press forming cannot produce highly dense green compacts. Here, we developed a new press forming‐based, room‐temperature process, the mega‐press forming (MF) method, that produces highly dense aggregate oxide films at a pressure below 1 GPa, which is lower than that at which oxide particles fracture, by taking advantage of the differences in cohesive force between microsized and nanosized particles. We used our novel process to produce highly dense lead zirconate titanate aggregate films on aluminum foil at room temperature, and found that when impregnated with silicone oil, these films exhibited low leakage current density and saturated polarization hysteresis properties. Furthermore, we were able to produce films with a porosity of only 6%, which is much lower than that of films produced by conventional press forming (20%). Thus, the MF method will be useful for the development of novel functional composite ceramics that are difficult to fabricate using high‐temperature processes.

We report grain orientation control for bismuth layer-structured ferroelectrics (BLSFs) films deposited by aerosol deposition (AD) method at room temperature. Bi ₄ Ti ₃ O ₁₂ (BiT), SrBi ₂ Ta ₂ O ₉ (SBTa), and SrBi ₄ Ti ₄ O ₁₅ (SBTi) starting powders with particles of various shape (plate-like, spherical, and angular) were prepared by solid-state reaction and fused salt synthesis. Their AD films represented fine microstructures without pores, which agrees well with previous reports. Although the SBTa AD films deposited by using spherical particles exhibited an extremely low Lotgering factor ( F ), the BiT AD films deposited by using plate-like particles exhibited a marked c -axis orientation. The F of BiT and SBTi AD films decreased with increasing film thickness ( t ). We consider that the dispersion of agglomerated plate-like particles on the film surface and the densification of the compacted powder layer occurring while under particle impact are important in obtaining the grain-oriented AD films. These results of using the AD method with shape-controlled particles are expected to result in open up an innovative functional coating technique.

We report aerosol deposition (AD) method for preparation of bismuth layer-structured ferroelectric thick films with enhanced ferroelectric and insulating properties. Constitution phase, crystal structure, polarization and leakage current properties of SrBi2Ta2O9 (SBTa) thick films with thickness of 2–4 µm were investigated. While obtained as-deposited SBTa films have slight c-axis grain orientation, the degree of orientation for the films annealed at higher than 1000 °C was the same as that for sintered bulks. Fracture cross-sectional scanning electron microscopy (SEM) images revealed that the as-deposited SBTa films on glass substrates had a fully dense microstructure. The low leakage current density (J) of less than 10-7 A/cm2 at 1 MV/cm was observed for SBTa films annealed at less than 900 °C, and the SBTa films annealed at 900 °C indicated a remanent polarization (Pr) of 5.7 µC/cm2, which is larger than that of sintered bulks (Pr of 4.7 µC/cm2) fabricated by conventional solid-state reaction using the same starting raw powder used for the AD method.

We report aerosol deposition (AD) method for preparation of bismuth layer-structured ferroelectric thick films with enhanced ferroelectric and insulating properties. Constitution phase, crystal structure, polarization and leakage current properties of SrBi₂Ta₂O₉ (SBTa) thick films with thickness of 2–4 µm were investigated. While obtained as-deposited SBTa films have slight c-axis grain orientation, the degree of orientation for the films annealed at higher than 1000 °C was the same as that for sintered bulks. Fracture cross-sectional scanning electron microscopy (SEM) images revealed that the as-deposited SBTa films on glass substrates had a fully dense microstructure. The low leakage current density (J) of less than 10^-7 A/cm² at 1 MV/cm was observed for SBTa films annealed at less than 900 °C, and the SBTa films annealed at 900 °C indicated a remanent polarization (P _r) of 5.7 µC/cm², which is larger than that of sintered bulks (P _r of 4.7 µC/cm²) fabricated by conventional solid-state reaction using the same starting raw powder used for the AD method.