Showing papers by "Renchao Che published in 2012"

Microwave Absorption Enhancement of Multifunctional Composite Microspheres with Spinel Fe3O4 Cores and Anatase TiO2 Shells

Abstract: Multifunctional composite microspheres with spinel Fe(3)O(4) cores and anatase TiO(2) shells (Fe(3)O(4)@TiO(2)) are synthesized by combining a solvothermal reaction and calcination process. The size, morphology, microstructure, phase purity, and magnetic properties are characterized by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, electron energy loss spectroscopy, powder X-ray diffraction, and superconducting quantum interference device magnetometry. The results show that the as-synthesized microspheres have a unique morphology, uniform size, good crystallinity, favorable superparamagnetism, and high magnetization. By varying the experimental conditions such as Fe(3)O(4) size and concentration, microspheres with different core sizes and shell thickneses can be readily synthesized. Furthermore, the microwave absorption properties of these microspheres are investigated in terms of complex permittivity and permeability. By integration of the chemical composition and unique structure, the Fe(3)O(4)@TiO(2) microspheres possess lower reflection loss and a wider absorption frequency range than pure Fe(3)O(4). Moreover, the electromagnetic data demonstrate that Fe(3)O(4@TiO(2) microspheres with thicker TiO(2) shells exhibit significantly enhanced microwave absorption properties compared to those with thinner TiO(2) shells, which may result from effective complementarities between dielectric loss and magnetic loss. All the results indicate that these Fe(3)O(4)@TiO(2) microspheres may be attractive candidate materials for microwave absorption applications.

Direct Imaging the Upconversion Nanocrystal Core/Shell Structure at the Subnanometer Level: Shell Thickness Dependence in Upconverting Optical Properties

Abstract: Lanthanide-doped upconversion nanoparticles have shown considerable promise in solid-state lasers, three-dimensional flat-panel displays, and solar cells and especially biological labeling and imaging. It has been demonstrated extensively that the epitaxial coating of upconversion (UC) core crystals with a lattice-matched shell can passivate the core and enhance the overall upconversion emission intensity of the materials. However, there are few papers that report a precise link between the shell thickness of core/shell nanoparticles and their optical properties. This is mainly because rare earth fluoride upconversion core/shell structures have only been inferred from indirect measurements to date. Herein, a reproducible method to grow a hexagonal NaGdF4 shell on NaYF4:Yb,Er nanocrystals with monolayer control thickness is demonstrated for the first time. On the basis of the cryo-transmission electron microscopy, rigorous electron energy loss spectroscopy, and high-angle annular dark-field investigations ...

General synthesis of xLi2MnO3·(1 − x)LiMn1/3Ni1/3Co1/3O2 nanomaterials by a molten-salt method: towards a high capacity and high power cathode for rechargeable lithium batteries

Abstract: Well-crystallized and high-performance xLi2MnO3·(1 − x)LiMn1/3Ni1/3Co1/3O2 (x = 0.3, 0.5, and 0.7) structurally integrated nanomaterials are prepared by a facile molten-salt strategy. The effects of heat-treatment temperature, time, and the molar ratio of KCl flux to reaction precursor on the particle size as well as the electrochemical properties are explored. Our results demonstrate that a 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 electrode delivers a high reversible capacity of 313 mA h g−1 with significant enhancement in the initial coulombic efficiency (87%) at room temperature, exhibits superior rate capability and shows improved electrochemical properties over a wide temperature range, in particular at low temperature.

Hierarchical magnetic yolk–shell microspheres with mixed barium silicate and barium titanium oxide shells for microwave absorption enhancement

Abstract: A facile “hydrothermal-assisted crystallization” route for the synthesis of hierarchical magnetic yolk–shell microspheres with mixed barium silicate and barium titanium oxide shells has been developed. Various yolk–shell microspheres with different shell thicknesses and core sizes have been successfully synthesized by controlling the synthetic parameters. The as-synthesized yolk–shell microspheres possess high magnetization, tailored shells, large specific surface area and high porosity, and are demonstrated to be attractive candidate materials for microwave absorption enhancement. Moreover, a possible formation mechanism based on the sacrificial-templating crystallization, dissolution–precipitation and in situ transformation processes is proposed.