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951.
The local structure and the g factor (gx, gy, and gz) of the Ni+ center in KTaO3 are theoretically studied using the perturbation formulas of the g factors for a 3d9 ion in orthorhombically elongated octahedra. The orthorhombic field parameters are determined from the superposition model and the local geometry of the system. In view of the covalency, the contributions from the ligand orbital and spin–orbit coupling interactions are taken into account from the cluster approach. In the calculations, the orthorhombic center is attributed to Ni+ occupying the host Ta5+ site, associated with the nearest-neighboring oxygen vacancy VO along the c-axis. Furthermore, the planar Ni+–O2− bonds are found to experience the relative variation ΔR (≈0.076 Å) along the a- and b-axis, respectively, due to the Jahn–Teller effect and the size mismatching substitution of Ta5+ by Ni+. Meanwhile, the effectively positive VO can make the central Ni+ displace away from VO along the c-axis by about 0.20 Å. The calculated g factors based on the above local distortions show good agreement with the experimental data. 相似文献
952.
Yue Tian Baojiu Chen Bining Tian Jiashi Sun Xiangping Li Jinsu Zhang Lihong Cheng Haiyang Zhong Hua Zhong Qingyu Meng Ruinian Hua 《Physica B: Condensed Matter》2012,407(13):2556-2559
Micro-sized NaY(MoO4)2:Tb3+ phosphors with dendritic morphology was synthesized by a ionic liquid-assisted hydrothermal process. X-ray diffraction (XRD) indicated that the as-prepared product is pure tetragonal phase of NaY(MoO4)2. Field emission scanning electron microscopy (FE-SEM) images showed that the as-prepared NaY(MoO4)2:Tb3+ phosphors have dendritic morphology. The photoluminescent (PL) spectra displayed that the as-prepared NaY(MoO4)2:Tb3+ phosphors show a stronger green emission with main emission wavelength 545 nm corresponding to the 5D4→7F5 transition of Tb3+ ion, and the optimal Tb3+ doping concentration for obtaining maximum emission intensity was confirmed to be 10 mol%. Based on Van Uitert's and Dexter's models the electric dipole–dipole (D–D) interaction was confirmed to be responsible for the concentration quenching of 5D4 fluorescence of Tb3+ in the NaY(MoO4)2:Tb3+ phosphors. The intrinsic radiative transition lifetime of 5D4 level is found to be 0.703 ms. 相似文献
953.
Cui-E Hu Zhao-Yi Zeng Chun-Yang Kong Yu-Ting Cui Lin Zhang 《Physica B: Condensed Matter》2012,407(24):4671-4675
We employ the spin-polarized generalized gradient approximation within the density functional theory to investigate the equation of state, magnetism and elastic constant of cubic ACrO3 (A=Pb, Ca, Sr, and Ba) perovskite. The antiferromagnetic phase is the most stable state at zero pressure. Under pressure, the ferromagnetic state will transform to the non-magnetic state. Considering the effect of magnetism, the equilibrium lattice constant, the bulk modulus and the high pressure equations of state agree well with the available experiments. By using the energy-strain method, the predicted elastic properties are satisfactory. 相似文献
954.
The paper briefly describes a one-dimensional dynamic model of plastic shear deformation in a material surface layer in sliding friction, giving grounds to the reduction of the problem dimension from 3D to 1D. A selection of simulation results is presented to illustrate the peculiarities of plastic deformation under the action of two competitive processes — work hardening and thermal softening due to frictional heating. Presented also are experimental data on which to base the conclusion on the possibility of surface layer flow similar to flow of a viscous fluid. To assess from the Reynolds number whether turbulization of the surface layer is feasible, simulation results are used. 相似文献
955.
956.
P. Zhao D.S. Liu Y. Zhang Y. Su H.Y. Liu S.J. Li G. Chen 《Solid State Communications》2012,152(12):1061-1066
Using first-principles density functional theory and non-equilibrium Green's function formalism for quantum transport calculation, we have investigated the electronic transport properties of heteronanotubes by joining a zigzag (6,0) carbon nanotube and a zigzag (6,0) boron nitride nanotube with different atomic compositions and joint configurations. Our results show that the atomic composition and joint configuration affect strongly the electronic transport properties. Obvious negative differential resistance behavior and large rectifying behavior are obtained in the heterostructure with certain composition and joint configuration. Moreover, tube length and tube radius can affect strongly the observed NDR and rectifying behaviors. The observed negative differential resistance and rectifying behaviors are explained in terms of the evolution of the transmission spectrum with applied bias combined with molecular projected self-consistent Hamiltonian states analysis. 相似文献
957.
A facile strategy has been developed for the preparation of bimetallic gold–silver (Au–Ag) nanocomposite films by alternating absorption of poly-(ethyleneimine)–silver ions and Au onto substrates and subsequent reduction of the silver ions. The composition, micro-structure and properties of the {PEI–Ag/Au}n nanocomposite films were characterized by ultraviolet visible spectroscopy (UV–vis), transmisson electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), surface enhanced Raman scattering (SERS) and cyclic voltammetry (CV). The UV–vis characteristic absorbances of {PEI–Ag/Au}n nanocomposite thin film increase almost linear with the number of bilayers, which indicates a process of uniform assembling. Appearance of a double plasmon bands in the visible region and the lack of apparent core–shell structures in the TEM images confirm the formation of bimetallic Au–Ag nanoparticles. The result of XPS also demonstrates the existence of Ag and Au nanoparticles in the nanocomposite films. TEM and FESEM images show that these Ag and Au nanoparticles in the films possess sphere structure with the size of 20–25 nm. The resulting {PEI–Ag/Au}n films inherit the properties from both the metal Ag and Au, which exhibits a unique performance in SERS and electrocatalytic activities to the oxidation of dopamine. As a result, the {PEI–Ag/Au}n films are more attractive compared to {PEI–Ag/PSS}n and {PEI/Au}n films. 相似文献
958.
Yongjian Zhang Zhengtang Liu Liping Feng Duyang Zang 《Applied Surface Science》2012,258(14):5354-5359
We have studied the electrical and optical properties of Cu–Al–O films deposited on silicon and quartz substrates by using radio frequency (RF) magnetron sputtering method under varied oxygen partial pressure PO. The results indicate that PO plays a critical role in the final phase constitution and microstructure of the films, and thus affects the electrical resistivity and optical transmittance significantly. The electrical resistivity increases with the increase of PO from 2.4 × 10?4 mbar to 7.5 × 10?4 mbar and afterwards it decreases with further increasing PO up to 1.7 × 10?3 mbar. The optical transmittance in visible region increases with the increase of PO and obtains the maximum of 65% when PO is 1.7 × 10?3 mbar. The corresponding direct band gap is 3.45 eV. 相似文献
959.
Cheng Wang Xiangxiong Zhang Chi-Wang Shu Jianguo Ning 《Journal of computational physics》2012,231(2):653-665
One of the main challenges in computational simulations of gas detonation propagation is that negative density or negative pressure may emerge during the time evolution, which will cause blow-ups. Therefore, schemes with provable positivity-preserving of density and pressure are desired. First order and second order positivity-preserving schemes were well studied, e.g., [6], [10]. For high order discontinuous Galerkin (DG) method, even though the characteristicwise TVB limiter in [1], [2] can kill oscillations, it is not sufficient to maintain the positivity. A simple solution for arbitrarily high order positivity-preserving schemes solving Euler equations was proposed recently in [22]. In this paper, we first discuss an extension of the technique in [22], [23], [24] to design arbitrarily high order positivity-preserving DG schemes for reactive Euler equations. We then present a simpler and more robust implementation of the positivity-preserving limiter than the one in [22]. Numerical tests, including very demanding examples in gaseous detonations, indicate that the third order DG scheme with the new positivity-preserving limiter produces satisfying results even without the TVB limiter. 相似文献
960.
Digital image processing for fringe patterns is an important procedure in optical interferometry. Filtering off noise from fringe patterns is one of the key tasks for extraction of the phase field. Spin filters proposed by Yu et al. [Appl. Opt. 33(1994), 41(2002), et al.] have been proven to be effective denoising methods. In this paper, we develop a nonlocal self-similarity filter, which averages similar pixels searched for in whole image instead of in a local fringe direction as the spin filters do. Although simple and free of the fringe orientation estimation, involving more pixels with higher similarity levels, our algorithm has stronger robustness against noise and thus denoises fringe patterns more effectively. Simulation and experimental results show that our algorithm outperforms related filters both in preserving smooth fringes and in reducing blurring effects and quantitative errors. 相似文献