Papers by Author: Li Ben Li

Abstract: (1-x)SnO₂-xZn₂SnO₄ composite ceramics were prepared by traditional ceramic processing and the varistor, dielectric properties were investigated. With increasing Zn₂SnO₄ content, the breakdown electrical field E_B and nonlinear coefficient α reaches the minimum of 6.9 V/mm and 2.5 at x=0.206, respectively. In the dielectric spectra, the relative dielectric constant ε_r exhibits strong frequency dependent character and at 40 Hz, ε_r for the sample of x=0.206 reaches a maximum as high as 3×10⁴. In the frequency region lower than 1 kHz, accompanied by the sharp increase of dielectric loss at 40 Hz, ε_r is depressed and a dielectric peak is presented in the spectra with increasing bias voltage. In the low electrical current range of 1.37-20 μA, The barrier height φ_B about 1.0 eV are obtained and it is found that φ_B decreases with increasing measuring current for each sample. Based on the results, the varistor behavior with high dielectric constant is explained by the Schottky barriers at grain boundaries.

Abstract: The effects of Y₂O₃ and In₂O₃ on the microstructure and electrical properties of SnO₂-based varistors were investigated. It was observed that the grain size of the samples decreased with doping Y₂O₃ and In₂O₃ and accordingly, the breakdown electrical field E_B increased greatly. The measurements of barrier height and grain size reveal that the variation of grain size was not the only reason for the change of electrical properties of the sample doped with In₂O₃ and, the improvement of nonlinear coefficient α may mainly attribute to the increase of barrier height. Some energy levels of different state defects on the grain boundary were obtained and the energy about 0.15 eV detected here of all the samples may be attributed to the activation of . The different effects of doping Y₂O₃ and In₂O₃ indicate that In₂O₃ is more effective to improve nonlinear electrical behavior and breakdown electrical field of SnO₂-based varistors.

Abstract: Single-phase BiFeO₃ (BFO) nano-crystallites were successfully synthesized in the temperature range of 500  750 oC by a simple diluted HNO3 sol method. During the crystallization process no intermediate phases were observed. As an example, we studied the electronic structure and thermodynamic stability of the BFO nano-crystallites calcined at 750 oC by X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC). The XPS showed that the oxidation state of Fe is Fe3+. The DSC indicated a novel exothermic peak at about 769 oC during cooling, which might be due to Bi2Fe4O9 or some other phases produced in the decomposition of BFO at high temperature.

Abstract: We propose a four-terminal nano device made of quantum wires with Rashba spin-orbit (SO) coupling. In each terminal there are several independent channels formed with quantum wires. The coherent transmission of electrons in such a nano system is a combined effect of quantum interference and spin precession. When defining two opposite terminals as source and drain leads, the charge and spin currents in channels of other two terminals exhibit spatial distributions which reflect the competition between spin precession and quantum interference during the tunneling of electrons. Since the four-terminal nano device is geometrically simple for the moving paths of charge and spin, our investigation may shed some light on the basic physical picture on this issue.

Abstract: MoO₃ nanorods were synthesized by a solution method with stirring and ultrasound. The formation temperature of MoO₃ nanorods were studied by XRD. The particle-size and morphology were characterized by TEM. The diameter of nanorods was ca. 60nm.

Abstract: A set of gradient stresses is used in Landau thermodynamic theory to explain the dielectric diffusion of BaTiO3 films grown on thick copper foils. Every grain in the films is treated as a single domain core that is surrounded by boundaries with low dielectric constant. The dielectric diffusion is mainly induced by the diffusive phase transition caused by the gradient stresses. The low dielectric constant boundaries suppress the peak value of the dielectric constant. The results agree with the experiments.

Abstract: CaCu3Ti4O12 ceramics were prepared by the traditional solid-state reaction method and the dielectric properties were investigated, the activation energy and relaxation time factor of the samples were calculated. Debye relaxation theory was attempted to analyze the experimental datum, the static and high-frequency dielectric constants were obtained according to Cole-Cole spectra. The temperature dependence of the dielectric constant of CaCu3Ti4O12 were fitted by computer and the theoretical results nearly agree with experimental results.

Abstract: CaCu3Ti4O12 and CaCu3Ti3.9Zr0.1O12 ceramics were prepared by the traditional solid-state reaction method and the dielectric properties were investigated. Comparison of the results of the two samples examined indicated that the partial replacement of titanium by zirconium in the system CaCu3Ti4O12 may result in different changes of the dielectric constant and dielectric loss. For these experimental phenomena possible explanations and predictions also have been presented.