Papers by Author: Tong Wei Li

Abstract: The electronic structures of the titanium-doped cubic perovskite ruthenates BaRu_1-xTi_xO₃ with x=0.125, 0.25, 0.375, 0.5, 0.625, 0.75, and 0.875 are investigated using the spin-polarized density functional theory within the pseudopotential plane wave method. It is found that a half-metallic phase appears in the 0.75- and 0.875-doped systems, and the origin of half-metallic property is the decrease of t_2g bandwidth of Ru 4d states with the increase in x. In addition, the energy gap of BaRu_0.25Ti_0.75O₃ is as large as 1.7 eV at the Fermi level in the up-spin density of states, which suggests a stable half-metallic phase can be obtained in the present systems.

Abstract: Studies of ion motion in crystalline and glassy materials, Jonscher power law, which was frequently referred to as the so-called universal dynamic response (UDR) is an effective method, but the power law exponents obtained from curve-fitting are sensitively affected by the frequency window employed in the analysis. So how to choose frequency window and which window can truly describe the nature of the materials, are important for every researcher. In this paper, through analyzing the experimental data of frequency dependence of ac conductivity in 50Li₂O–50P₂O₅ glasses, a simple method to choose frequency window was found and further discussions indicated our choice was reasonable.

Abstract: Four kinds of three-dimensional structure of graphane are investigated using first-principles method. It is found that the energy of four different structures has little difference, so the conclusion can be drawn that the four structures are likely to exist synchronously in experiments.

Abstract: Based on Jonscher power law, frequency dependence of ac conductivity of 40Fe2O3–60P2O5 glasses were investigated in a relatively high temperature range. Results indicated the power law exponent first decreases with increasing temperature, reached a minimum at a certain temperature and then in- creases again. Preliminary theoretical explanations and predictions for this phenomenon were presented.

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: Performing ab-initio total-energy calculations to investigate the adsorption and diffusion processes of the Au atoms with both the clean Si(001)-(1×1) and H-terminated Si(001)-(2×1) surfaces. It was found that, on the clean Si(001)-(1×1) surface, the most stable adsorption sites for Au atoms are middle part of four Si atoms, while on H-terminated Si(001)-(2×1) surface, the most stable sites are the middle part of a Si-Si dimer. The result showed that surface hydrogenation make most stable site transfer and affect the adsorption of Au on Si(001) surface.

Abstract: The electrical properties of 10M2O-36Fe2O3-54P2O5 (M=Li, Na and K) glasses were studied in the temperature range from 323 to 573 K. Non-linear Arrhenius behavior was observed for all the samples examined. It was shown that in both high- and low-temperature ranges, the replacement of Li, Na and K would result in decreases in both the dc conductivity and the activation energy. Analysis of the relationship of the parameters included in the Arrhenius equation, activation energy and the pre- exponential factor for each sample, preliminary explanations for these experimental phenomena have been presented.

Abstract: SiC films were prepared by HFCVD technique on (111) Si substrate. The composition and the structure of the films were investigated using EDX, XRD and transient fluorescence. Results indicated the films deposited were nanocrystalline and the calculation of the grain size gave a further confirmation. PL measurement of the present films showed that there existed a strong ultraviolet emission at room temperature.

Abstract: The adsorption of Au on clean Si(001) surface is investigated by the local density approximation using first-principles pseudopotentials. We found that the adsorption energy of Au on ideal Si(001)-(1×1) surface is lower than that on reconstructed Si(001)-(2×1) surface, suggesting that adsorbed Au atoms chemically react with the surface Si atoms and break Si-Si dimer bonds of the substrate. Furthermore, the intermixing of Au and Si is also considered and the calculation suggests that intermixing will not take place at low temperature. But due to the small energy barrier for Au atoms to diffuse into Si substrate, we can conclude that the Au-Si alloy is easily formed at relatively high temperature. This result should be one of the reasons of the lack of consensus on the issue of intermixing of Au and Si.