Designing a Periodic Structure with a Composition Gradient Stack Unit to Realize a Good Comprehensive Dielectric Property of Yttrium Iron Garnet Multilayer Film.

Y3Fe5O12 (YIG) thin films are highly needed in microwave devices, but the low saturation magnetization and low dielectric constant greatly limit the application of YIG thin films. It was reported that the ion substitution, for example, Pr3+, could increase the dielectric constant of Y3-xPrxFe5O12 (YPrxIG). Unfortunately, the dielectric loss would also be significantly increased. In this work, [YPr0.20IG/YPr0.15IG/YPr0.10IG]N multilayer films were fabricated via the chemical solution deposition method, by designing a periodic structure with the [YPr0.20IG/YPr0.15IG/YPr0.10IG] composition gradient stack. In comparison to the average composition of YPr0.15IG, high saturation magnetization, high dielectric constant, and low loss were successfully simultaneously achieved in the multilayer structure. The N = 6 film exhibited a higher saturation magnetization of 252.8 emu/cm3 than the value (213.1) of the YPr0.15IG (average composition) film. The dielectric constant of the N = 6 film reached 25.6 in contrast to the value of 18.3 for the YPr0.15IG film at 12.4 GHz, which was the contribution of the rapid flip of the electric dipole of a single-unit dielectric material and the accumulation of interface charge. Furthermore, the dielectric loss of the film with N = 6 decreased to 0.0036 compared with the value (0.0102) of the average composition film. This work demonstrated a strategy of designing a periodic structure with a composition gradient stack unit to realize a good comprehensive dielectric property through taking advantage of the multiple effects of "coherent growth, component matching, and interface accumulation".

3D hollow NiCo LDH nanocages anchored on 3D CoO sea urchin-like microspheres: A novel 3D/3D structure for hybrid supercapacitor electrodes.

The research on the structure of advanced electrode materials is significant in the field of supercapacitors. Herein, for the first time, we propose a novel 3D/3D composite structure by a multi-step process, in which 3D hollow NiCo LDH nanocages are immobilized on 3D sea urchin-like CoO microspheres. Results show that the 3D CoO acts as an efficient and stable channel for ion diffusion, while the hollow NiCo LDH provides abundant redox-active sites. The calculated results based on density function theory (DFT) show that the CoO@NiCo LDH heterostructure has an enhanced density of states (DOS) near the Fermi level and strong adsorption capacity for OH-, indicating its excellent electrical conductivity and electrochemical reaction kinetics. As a result, the CoO@NiCo LDH electrode has an areal specific capacity of 4.71C cm-2 at a current density of 3 mA cm-2 (440.19C g-1 at 0.28 A g-1) and can still maintain 88.76 % of the initial capacitance after 5000 cycles. In addition, the assembled hybrid supercapacitor has an energy density of 5.59 mWh cm-3 at 39.54 mW cm-3.

Hierarchy structure and fracture mechanisms of the wild wolf tusk's enamel.

The self-growth and self-strengthening of natural biomaterials provided us strategies for new materials design. In this paper, the microstructure and fracture mechanisms of the wild wolf tusk's enamel were studied. The enamel included four-order hierarchies, which were the hydroxyapatite (HAP) fiber (first-order, nano-scale, ploy-crystals), enamel rod (second-order, micro-scale, rope-like), enamel type (third-order, meso-scale, mat-like) and the enamel patterns (forth-order, macro-scale), respectively. It was interesting to find that the numerous nano-grains distributed disorderly in a single HAP fiber. The thousands HAP fibers bundled together to form the rope-like enamel rod. The protein ligaments were discovered between adjacent enamel rods. The out enamel, inner enamel and P&D-zones showed a criss-cross type and ran through whole enamel pattern in three-dimensional space. The enamel of the wild wolf tusk exhibited an excellent fracture toughness based on the nanoindentation tests. The fracture morphology in transverse direction indicated that the cracks preferred to propagate along the weak interface (protein or interrod) and cut those enamel rods perpendicular to the propagation direction. However, the cracks extended obviously forward along the step-like paths from the outmost surface of the enamel to the enamel-dentin junction in the longitudinal direction. It was considered that the protein ligament was the main reason for the good fracture toughness of the bulk enamel. Our studies reveal that the design strategies of the natural material can be applied to guide the development of high-performance artificial materials.

Wild boar's tusk enamel: Structure and mechanical behavior.

Natural bio-ceramics have attracted extensive interests due to its high strength and high toughness, which can hardly be achieved in artificial ceramics simultaneously. In this work, the microstructure and properties of the wild boar's tusk enamel were investigated. The enamel was found to exhibit a hierarchical structure ranging from the hydroxyapatite (HAP) fibers (single or poly-crystals, nano-scale), enamel rods (micro-scale), enamel types (meso-scale) to enamel patterns (macro-scale). It is worth mentioning that the high-density and high-order hierarchical nanotwins were observed in the HAP fibers. The mechanical properties of the wild boar's tusk enamel showed strong anisotropy and were higher along the longitudinal direction than along the transverse direction. The mechanical properties varied from the dentin-enamel junction (DEJ) to the outer surface. The elastic modulus increased with the distance from the DEJ and then kept invariant. The nano-hardness increased in inner enamel but decreased in outer enamel. There was a peak of nano-hardness in inner enamel area. The fracture toughness showed an opposite tendency. It exhibited high values in inner enamel, but fell in the outer enamel zone. The irregular, decussating texture of the enamel, as well as the nanotwins/hierarchical nanotwins was considered as the main reason for its excellent mechanical properties. These unique structures of the wild boar's tusk enamel are expected to cast light on the design of medical materials and provide some guidelines to improve their mechanical properties.