BNKT Ceramics, one of the representative Pb free based piezoelectric ceramics, constitutes a perovskite(ABO3) structure. At this time, the perovskite structure (ABO3) is in the form where the corners of the octahedrons are connected, and in the unit cell, two ions, A and B, are cations, A ion is located at the body center, B ion is located at each corner, and an anion O is located at the center of each side. Since Bi, Na, and K sources constituting the A site are highly volatile at a sintering temperature of 1100℃ or higher, it is difficult to maintain uniformity of the composition. In order to solve this problem, there should be suppression of volatilization of the A site material or additional compensation of the volatilized. In this study, the basic composition of BNKT Ceramics was set to Bi0.5(Na0.78K0.22)0.5TiO3 (= BNKT), and volatile site (Bi, Na, and K sources) were coated in the form of a shell to compensate additionally for the A site ions. In addition, the physical and electrical properties of BNKT and its coated with shell additives(= @BNK) were compared and analyzed, respectively. As a result of analyzing the crystal structure through XRD, both BNKT(Core) and @BNK(Shell) had perovskite phases, and the crystallinity was almost similar. Although the Curie temperature of the two sintered bodies was almost the same (TC = 290 ~ 300 ℃), it was confirmed that the d33 (piezoelectric coefficient) and Pr (residual polarization) values were different. The experimental results indicated that the additional compensation for a shell additive causes the coarsening, resulting in a decrease in sintering density and Pr(remanent polarization). However, coating shell additives to compensate for A site ion is an effective way to suppress volatilization. Based on these experimental results, it would be the biggest advantage to develop an eco-friendly material (Lead-free) that replaced lead (Pb), which is harmful to the human body. This lead-free piezoelectric material can be applied to a biomedical device or products(ex. earphones (hearing aids), heart rate monitors, ultrasonic vibrators, etc.) and skin beauty improvement products (mask packs for whitening and wrinkle improvement).

We report the behaviour of carbon black (CB) nanoparticles (spherical carbon shells), subjected to external pressure, using diamond anvil cell at synchrotron facility. CB nanoparticles have been synthesized by lamp black method using olive oil as combustion precursor and ferrocene as an organometallic additive. The catalyst-assisted CB has an iron oxide (γ-Fe2O3) core and amorphous carbon shell (i.e. core–shell structure). Our present study suggests that the carbon shells are partially transparent to the applied high pressure, and result in the reduction of effective pressure that gets transferred to the iron oxide core. High-pressure Raman spectroscopy results indicate that the surrounding carbon shells get compressed with pressure and this change is reversible. However, no structural transformation was observed till the highest applied pressure (25 GPa). The Raman spectroscopy results also suggests that the carbon shells are less pressure sensitive as their pressure coefficients (dω/dP) of G-peak were calculated (3.79 cm− 1/GPa) to be less than that for other carbon allotropes.

The capacity of high nickel Li(NixCoyMn1-x-y)O2 (NCM, x ≥ 0.8) cathodes is known to rapidly decline, a serious problem that needs to be solved in a timely manner. It was reported that cathode materials with the {010} plane exposed toward the outside, i.e., a radial structure, can provide facile Li+ diffusion paths and stress buffer during repeated cycles. In addition, cathodes with a core-shell composition gradient are of great interest. For example, a stable surface structure can be achieved using relatively low nickel content on the surface. In this study, precursors of the high-nickel NCM were synthesized by coprecipitation in ambient atmosphere. Then, a transition metal solution for coprecipitation was replaced with a low nickel content and the coprecipitation reaction proceeded for the desired time. The electrochemical analysis of the core-shell cathode showed a capacity retention of 94 % after 100 cycles, compared to the initial discharge capacity of 184.74 mA h/g. The rate capability test also confirmed that the core-shell cathode had enhanced kinetics during charging and discharging at 1 A/g.

Silver/graphene core/shell nanocomposites were synthesized through a one-step electric explosion of wire method using only silver wires and ethanol. The morphology of the graphene shell structures can be easily formed by alternating the solvent from deionized water to ethanol. Transmission electron microscopy revealed that the size of the prepared silver/graphene core/ shell nanocomposites was in the 10–110 nm range. The Raman spectra showed the formation of graphene shells on silver. A possible formation mechanism of the silver/graphene core/shell nanocomposites is proposed in this study. The crystallinity of the nanoparticles was investigated via X-ray diffraction. The graphene on the surfaces of the nanocomposites containing functional groups was analyzed through Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. Zeta potential and dynamic light scattering analyses were performed to determine the dispersion characteristics of the nanocomposites when redispersed in other solvents.

In this study, effect of core-shell structure on compaction behavior of harmonic powder is investigated. Harmonic powders are made by electroless plating method on Fe powders. Softer Cu shell encloses harder Fe core, and the average size of Fe core and thickness of Cu shell are 34.3 μm and 3.2 μm, respectively. The powder compaction procedure is processed with pressure of 600 MPa in a cylindrical die. Due to the low strength of Cu shell regions, the harmonic powders show better densification behavior compared with pure Fe powders. Finite element method (FEM) is performed to understand the roll of core-shell structure. Based on stress and strain distributions of FEM results, it is concluded that the early stage of powder compaction of harmonic powders mainly occurs at the shell region. FEM results also well predict porosity of compacted materials.

Homogenous silica-coated samples with controlled silica thickness were synthesized by the reverse microemulsion method. First, 7 nm size cobalt ferrite nanoparticles were prepared by thermal decomposition methods. Hydrophobic cobalt ferrites were coated with controlled using polyoxyethylene(5)nonylphenylether (Igepal) as a surfactant, and tetraethyl orthosilicate (TEOS). The well controlled thickness of the silica shell was found to depend on the reaction time and the amount of surfactant used during production. Thick shell was prepared by increasing reaction time and small amount of surfactant.