[en] Nano powders with high reflectivity in near-infrared waveband have broad applications as thermal insulation materials. In this study, nano bismuth titanate powders with the reflectance to near-infrared of as high as 89.5% in average were prepared via a sol-gel method by using tetrabutyl titanate, bismuth nitrate as raw materials and citric acid, acetic acid as reaction adjuvant reagents. Furthermore, to control the reflectivity in the visible light waveband, the as-prepared nano bismuth titanate powders were further coated with nano-Ag by using NaBH₄ as a reduction agent. The influence of different dispersants on reflectivity and on powder dispersibility has also been studied. SEM characterization demonstrates that PEG1000, worked as a dispersant, significantly enhances the dispersion of bismuth titanate powders comparing with non-dispersant system. UV-Vis-NIR spectra reveal that with addition amount of AgNO₃ of 1.5 ml and PEG1000 as the dispersant, the Ag-coated bismuth titanate nano powders can reach about 60% of reflectance to near-infrared, while the reflectance of visible light can be controlled as low as around 14%. It is very promising for such nano powders to be used in thermal insulation glass materials. (paper)

[en] The magnetic polymer adsorbent Fe₃O₄@poly (m-phenylenediamine) (Fe₃O₄@PmPD) was formed at room temperature (25°C) by chemical oxidative polymerization using Fe₃O₄ and m-phenylenediamine (mPD). The effects of the Na₂CO₃ concentration and Fe₃O₄ mass used in the synthesis on the adsorption capacity were studied. The effects of contact time, initial concentration and temperature on adsorption were individually analyzed. The equilibrium data were evaluated by kinetic and thermodynamic models. The highest adsorption capacity of the material was 654.4 mg/g at room temperature and pH=2. Finally, the recyclability of the materials was tested by cycling experiments. The material could be recycled and retained 73.18% of its initial adsorption capacity after 5 cycles. The magnetic polymer material exhibits excellent hexavalent chromium removal capacity and broad application prospects in the treatment of chromium-containing wastewater. (paper)

[en] Anatase TiO₂ nanoparticles with different amounts of fluorine doping were synthesized by a hydrothermal method using hydrogen titanate nanotubes as a precursor and applied as mesoporous layer for preparing perovskite solar cell. The morphology and structures were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), meanwhile, the properties and performances were tested by photoluminescence spectrum (PL) and current density and voltage (J-V) curve. It was found that doping fluorine into TiO₂ made the photoelectric conversion efficiency (PCE) of perovskite solar cell (PSC) to be improved. The best PCE of PSC based on a F-doped TiO₂ was 13.06% and increased by 51% compared to an un-doped TiO₂. The study provided a direction for the exploration of high performance electron transport layer of perovskite solar cell. (paper)

[en] The stress intensity factor (SIF) of a multi-material magnetoelectroelastic wedge in anti-plane deformation is analytically determined by the symplectic method. The Lagrangian equations in configuration variables alone are transformed to Hamiltonian equations in dual variables (configuration and momentum) which allow the use of the method of separation of variables. The solutions of the Hamiltonian equations can be expanded analytically in terms of the symplectic eigenfunctions with coefficients to be determined by the boundary conditions. For the wedge problem, the pairs of anti-plane displacements and shear stresses, electric fields and electric displacements, and magnetic fields and magnetic inductions are proved to be the dual (momentum) variables of the configuration variables. The singularity orders depend directly on the first few eigenvalues whose real parts are less than one but greater than zero. Numerical results for various conditions show the variations of the singularity orders. In particular, special behaviors of the order of the singularity for some special wedge angles are noted. (paper)

[en] In tin dioxide nanostructures, oxygen vacancies (OVs) play an important role in their optical properties and thus regulation of both OV concentration and type via external strain is crucial to exploration of more applications. First-principle calculations of SnO_2 (110) surface disclose that asymmetric deformations induced by external strain not only lead to its intrinsic surface elastic changes, but also result in different OV formation energy. In the absence of external strain, the energetically favorable oxygen vacancies(EFOV) appear in the bridging site of second layer. When -3.5% external strain is applied along y direction, the EFOV moves into plane site. This can be ascribed that the compressed deformation gives rise to redistribution of electronic wave function near OVs, therefore, formation of newly bond structures. Our results suggest that different type OVs in SnO_2 surface can be controlled by strain engineering.

[en] A sodium bismuth titanate (Na_0.5Bi_0.5)TiO₃ (NBT) thin film of perovskite structure, synthesized by radio-frequency magnetron sputtering, exhibited a remanent polarization of 11.9 μC cm^-2 and a coercive field of 37.9 kV cm^-1 at room temperature. It however showed a rather high leakage current density of ∼6 x 10^-5 A cm^-2 at an applied electric field of 100 kV cm^-1. There occurs a change in the controlling mechanism of the electrical behaviours of the NBT thin film from grain interiors to grain boundaries with increasing temperature. The ac conductivity obeys the Jonscher relation. The activation energies for dc conductivity and hopping frequency of the charge carriers are calculated to be 0.92 eV and 1.00 eV, respectively, suggesting oxygen vacancies are the most likely charge carriers at high temperatures. Hopping of oxygen vacancies trapped at the grain boundaries and excitation of polarons in the grain interior are responsible for the relatively high dielectric loss and high dc conductivity. The contribution of hopping charge carriers to the dielectric response is demonstrated by the frequency dispersion observed for the relative permittivity in the low frequency region