Development of Bismuth Ferrite as a Piezoelectric and Multiferroic Material by Cobalt Substitution

Bismuth ferrite (BiFeO₃) is the most widely studied multiferroic material with robust ferroelectricity and antiferromagnetic ordering at room temperature. One of the possible device applications of this material is one that utilizes the ferroelectric/piezoelectric property itself such as ferroelectric memory components, actuators, and so on. Other applications are more challenging and make full use of its multiferroic property to realize novel spintronics and magnetic memory devices, which can be addressed electrically as well as magnetically. This progress report summarizes the recent attempt to control the piezoelectric and magnetic properties of BiFeO₃ by cobalt substitution.     

Fabricating transparent waveguide for wireless communication

The high frequency characteristics of hybrid structures made from indium tin oxide (ITO) films and very fine gold (Au) lines were theoretically and experimentally investigated to develop invisible coplanar waveguide (CPW) structures for microwave and millimeter-wave applications. After optimizing the Au/ITO hybrid structures, we achieved fabrication of an invisible CPW structure showing both high transmission and low reflection characteristics in the GHz range. Electromagnetic simulations by using a finite elements method explained the reason for the improved characteristics of the optimized Au/ITO hybrid CPW.     

Origin of Surface Coating Effect for MgO on LiCoO2 to Improve the Interfacial Reaction between Electrode and Electrolyte

Surface coating on lithium‐ion battery cathodes improves their durability at high potentials, which is a well‐known practical application. However, the mechanism is still unclear because the coating influences the electrode/electrolyte interface at a few nanometer‐scale and direct observation of the interface under real operating conditions of a battery is challenging. This study reveals the mechanism of the surface coating effect on lithium‐ion battery cathodes by using in operando X‐ray absorption spectroscopy (XAS) on well‐defined MgO‐coated LiCoO₂ thin‐film electrodes prepared via pulsed laser deposition. Total‐reflection in operando XAS measurements reveal that LiCoO₂ forms a reductive phase at the interface between the uncoated‐LiCoO₂ electrode and the electrolyte, while the MgO coating layer inhibits the redox process, leading to an improvement in the cycle performance of the battery. Depth‐resolved in operando XAS measurements indicate that a solid solution of the magnesium phase forms at the LiCoO₂ surface upon MgO coating. Magnesium ions function as pillars to stabilize the layered structure at the interface between the LiCoO₂ electrode and the electrolyte for delithiated states upon cycling at potentials.     

Waveguide for transmitting and radiating high-frequency, high-power ultrasound using higher mode vibrations of a cylindrical rod

It was shown that a cylindrical solid rod, with a diameter several times larger than the wavelength, can be used as an efficient waveguide for transmitting and radiating high-power ultrasound at higher frequencies. A number of cylindrical rods of varying size and material were tested, and their efficiency as a waveguide was evaluated by the measurements of mechanoacoustic efficiency when the radiating end of the rod was immersed in water for an acoustical load. As an example of waveguide application, a mock-up water atomizer was constructed and shown to work stably at a continuous input of 200 W at 500 kHz. As a consequence of analytical and experimental considerations of the higher mode vibrations of cylindrical rods, a diagram for the optimal design of the waveguides was constructed. For instance, an aluminum alloy rod 6.9 cm in diameter and 23.3 cm in length yielded a mechanoacoustic efficiency as high as 88% at 500 kHz. For high temperature applications, the cylindrical rod can be used as a radiator of heat, as well as for a separator of the piezoelectric transducer from the hot object.     

Effects of glass components on crystallization and dielectric properties of BST glass–ceramics

Crystallization behavior was studied for glass powders in which some portions of AlF₃ in the net composition of 60(Ba_0.7Sr_0.3)TiO₃–25SiO₂–15AlF₃ were replaced with Ga₂O₃ or Bi₂O₃. The replacement with Ga₂O₃ resulted in a progressive increase in crystallization temperature, which effectively assisted the viscous sintering of glass powders to produce densified BST glass–ceramics at relatively lower temperatures. For the Bi₂O₃-replaced glass powders, an increasing amount of Bi₂O₃ replacement lowered the crystallization temperature and yielded less densified glass–ceramics containing a considerable amount of glassy phase. The temperature dependence of permittivity was estimated for the Ga₂O₃- and Bi₂O₃-replaced glass–ceramics as a function of sintering conditions and the amount of replacement, respectively.     

Real-time ellipsometric characterization of the initial growth stage of poly(3,4-ethylene dioxythiophene): poly(styrene sulfonic acid) films by electrospray deposition

Kinetic spectroscopic ellipsometry have been used to study the initial growth stage of poly(3,4-polyethylene dioxythiophene):poly(styrenesulfonic acid)(PEDOT:PSS) films by the electrospray deposition (ESD) method. The real-time spectra analysis revealed that the surface overlayer decreased in thickness once the first bulk layer monolayer was formed, indicating a smoothening effect as the nucleation-related microstructure coalesced into the bulk layer. Once the coalescence was completed and the nucleation-induced surface roughness layer was stabilized, the underlying bulk layer increased linearly with time. These results originate from the degrees of the evaporation of solvent material during the transferring the precursors to the surface and/or of the diffusion of deposition precursors after sticking at the growing surface.     

Physicochemical Property of Huaishan (Rhizoma Dioscorea) and Matai (Eleocharis dulcis) Starches

The physicochemical properties of starch, the main component in tuberous root of Huaishan (Rhizoma Dioscorea) and corm of Matai (Eleocharis dulcis) was investigated and compared with those of a Japanese yam, “Yamanoimo” starch, and potato starch. Mean particle sizes of Huaishan and Matai starches were 24 ± 5 μm and 12 ± 5 μm, respectively. X-Ray diffraction pattern suggests that Huaishan starch was B-type or C-type just close to B-type and Matai starch was A-type or C-type just close to A-type. Apparently, the intermediate component (IntCom) of Huaishan starch, which was obtained by fractionation of the starch into amylose and amylopectin, may still contain amylose and amylopectin. IntCom of Matai starch has an intermediate nature between amylose and amylopectin. It is concluded that the amylopectin molecules of Huaishan starch contain a larger amount of longer branch-ed chains and those of Matai starch contain a larger amount of shorter branched chains. Amylograms of Matai and Huaishan starches suggest that the gelatinized starches are difficult to retrograde. Digestibility of Huaishan starch by an α-amylase was the highest among the tested starches.