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First-principles cluster calculations are reported of the local electronic structure of the three compounds: La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2. The copper
and the planar oxygen 2p
atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the
atomic orbital lowered significantly in energy for chlorine and fluorine apical positions. 相似文献
33.
B.L. Ahuja V. Sharma A.R. Jani 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,262(2):391-398
The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi 241Am Compton spectrometer. To compare the experimental data, we have computed the Compton profiles and energy bands using spin-polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) and density functional theory schemes. The experimental and theoretical data are also compared with the available augmented plane wave and linear combination of Gaussian orbitals calculations. The origin of anisotropy in the momentum densities is discussed in terms of the energy bands and the Fermi surface topology. Among the various model calculations, it is seen that the KKR calculations are in better agreement with the absolute profiles but they significantly overestimate the anisotropy in momentum densities. 相似文献
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A. S. Vorontsov L. A. Osminkina A. E. Tkachenko E. A. Konstantinova V. G. Elenskiĭ V. Yu. Timoshenko P. K. Kashkarov 《Semiconductors》2007,41(8):953-957
Infrared spectroscopy and electron spin resonance measurements are used to study the properties of porous silicon layers on adsorption of the I2 iodine molecules. The layers are formed on the p-an n-Si single-crystal wafers. It is established that, in the atmosphere of I2 molecules, the charge-carrier concentration in the layers produced on the p-type wafers can be noticeably increased: the concentration of holes can attain values on the order of ~1018?1019 cm?3. In porous silicon layers formed on the n-type wafers, the adsorption-induced inversion of the type of charge carriers and the partial substitution of silicon-hydrogen bonds by silicon-iodine bonds are observed. A decrease in the concentration of surface paramagnetic defects, P b centers, is observed in the samples with adsorbed iodine. The experimental data are interpreted in the context of the model in which it is assumed that both deep and shallow acceptor states are formed at the surface of silicon nanocrystals upon the adsorption of I2 molecules. 相似文献
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东莞电力局点对点数字微波传输网,主要负责省调,东莞局本部和所属220kV变电站的话音和远动数据的实时信息传输,以及为电力线载波通信提供汇集通道。由于各种原因,在运行中不能很好地满足东莞地区通信中心发展的要求。从提高运行可靠率和话路资源利用率两方面着手,在不需要很大 情况下,对该传输网进行改造,取得了比较满意的效果。 相似文献
36.
铌鲜酸铅弛豫型铁电陶瓷的介电老化行为研究 总被引:1,自引:0,他引:1
通过典型弛豫型铁电陶瓷铌镁酸铅介电老化行为的研究,发现高温区的Debye型弛豫过程与介电过程电老现象存在有机联系,指出复合钙钛矿弛豫型电体的结构缺陷特征对其介电老化起着重要作用,介电极化行为与老化行为对比分析和恒温经时老化研究表明,外的局域化电子和空穴对铁电微畴畴壁“钉扎”效应产生失电体介电化行为的快过程。 相似文献
37.
Ying Zhang Tianmin Wang 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(18):3200-3203
Using a first-principles method based on density functional theory, we have investigated energetics and site preference of helium (He) in a ferromagnetic bcc-iron (Fe) grain boundary (GB). We calculate the binding energies of He atom in the GB, which show that the substitutional He is energetically favored in comparison with the interstitial He with a small energy difference of 0.06 eV. The segregation energy is calculated to be ∼1.4 eV for the energetically favorable GB substitutional and interstitial sites, which is large enough for the He atoms to segregate to these sites, independent of the temperature and the bulk He concentration. This leads to the conclusion that all the He atoms will segregate into the GB at a typical temperature range of 573-1173 K. 相似文献
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Yogesh Kumar Manuel Herrera Fouran Singh S.F. Olive-Méndez D. Kanjilal Shiv Kumar V. Agarwal 《Materials Science and Engineering: B》2012,177(16):1476-1481
We report the room temperature cathodoluminescence and photoluminescence of swift ion irradiated (130 MeV Nickel ion) porous silicon zinc oxide nanocomposites. The evolution of a broad and flat emission band from 1.5 to 3.5 eV is demonstrated. Annealing effect of irradiation is found to result in a relative increase in the band edge emission. Emission wavelength can be tuned in the complete visible range by changing the substrate characteristics. 相似文献
40.
M.A. GhebouliB. Ghebouli A. Bouhemadou M. FatmiK. Bouamama 《Journal of Alloys and Compounds》2011,509(5):1440-1447
The structural, electronic, optical and thermodynamic properties of SrxCa1−xO, BaxSr1−xO and BaxCa1−xO ternary alloys in NaCl phase were studied using pseudo-potential plane-wave method within the density functional theory. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependence of the lattice parameters, band gaps, dielectric constants, refractive indices, Debye temperatures, mixing entropies and heat capacities on the composition x were analyzed for x = 0, 0.25, 0.50, 0.75 and 1. The lattice constant for SrxCa1−xO and BaxSr1−xO exhibits a marginal deviation from the Vegard's law, while the BaxCa1−xO lattice constant exhibits an appreciable upward bowing. A strong deviation of the bulk modulus from linear concentration dependence was observed for the three alloys. The microscopic origins of the gap bowing were detailed and explained. The composition dependence of the dielectric constant and refractive index was studied using different models. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds which may be a support for the results of the ternary alloys reported here for the first time. 相似文献