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1.
Lingli Wang Haiyong NiQiuhong Zhang Fangming Xiao 《Journal of Alloys and Compounds》2011,509(42):10203-10206
The electronic structure and linear optical property of BaSi2N2O2 (BSNO) have been calculated by density functional method with the local density approximation. A direct band gap of 5.17 eV at G is obtained for BSNO. The calculated total and partial densities of states indicate that the top valence band is mainly constructed from the N 2p and O 2p states, the low conduction band mostly originates from Ba 4d and Si 3p states. The calculated linear optical property of BSNO is in good agreement with the experimental measurement. 相似文献
2.
Ali Hussain Reshak I.V. KitykR. Khenata S. Auluck 《Journal of Alloys and Compounds》2011,509(24):6737-6750
An all electron full potential linearized augmented plane wave method, within a framework of GGA (EV-GGA) approach, has been used for an ab initio theoretical study of the effect of increasing tellurium content on the band structure, density of states, and the spectral features of the linear and nonlinear optical susceptibilities of the cadmium-selenide-telluride ternary alloys CdSe1−xTex (x = 0.0, 0.25, 0.5, 0.75 and 1.0). Our calculations show that increasing Te content leads to a decrease in the energy band gap. We find that the band gaps are 0.95 (1.76), 0.89 (1.65), 0.83 (1.56), 0.79 (1.44) and 0.76 (1.31) eV for x = 0.0, 0.25, 0.5, 0.75 and 1.0 in the cubic structure. As these alloys are known to have a wurtzite structure for x less than 0.25, the energy gaps are 0.8 (1.6) eV and 0.7 (1.55) eV for the wurtzite structure (x = 0.0, 0.25) for the GGA (EV-GGA) exchange correlation potentials. This reduction in the energy gaps enhances the functionality of the CdSe1−xTex alloys, at least for these concentrations, leading to an increase in the effective second-order susceptibility coefficients from 16.75 pm/V (CdSe) to 18.85 pm/V (CdSe0.75Te0.25), 27.23 pm/V (CdSe0.5Te0.5), 32.25 pm/V (CdSe0.25Te0.75), and 37.70 pm/V (CdTe) for the cubic structure and from 12.65 pm/V (CdSe) to 21.11 pm/V (CdSe0.75Te0.25) in the wurtzite structure. We find a nonlinear relationship between the absorption/emission energies and composition, and a significant enhancement of the electronic properties as a function of tellurium concentration. This variation will help in designing better second-order susceptibility materials by manipulating of the electronic structures of these materials with different compositions to achieve more delocalized atomic bonds. 相似文献
3.
Yu.V. Knyazev A.V. Lukoyanov Yu.I. Kuz’minA.G. Kuchin 《Journal of Alloys and Compounds》2011,509(17):5238-5241
Optical properties of intermetallic isostructural compounds LaNi5−xCux (x = 0, 0.6, 1, 1.2) have been studied in the spectral range from 0.22 to 15 μm using the ellipsometry method. It was found that the substitution of copper for nickel leads to local changes in the optical conductivity spectra. Theoretical calculations of the electronic structure and interband optical conductivity of LaNi5−xCux compounds with x = 0, 1, 2, 3 were performed in the generalized gradient approximation within the pseudopotential plane-wave method PWSCF. Both the optical spectroscopic measurements and theoretical calculations demonstrate the presence of a broad absorption band around 4 eV associated with the Cu 3d → Ni 3d electron transitions and increasing with the growth of copper content. 相似文献
4.
Using all electron full potential - linearized augmented plane wave (FP-LAPW) method the linear and nonlinear optical susceptibilities of cubic GaAs1−xBix alloys with x varying between 0.25 and 0.75 with increment of 0.25 are investigated. We have applied the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used. The reflectivity, refractivity, absorption coefficient and the loss function of these ternary alloys were investigated. The absorption coefficient shows that GaAs0.25Bi0.75 possess the highest coefficient among the investigated alloys which supports our previous observation that the band gap decreases substantially with increasing Bi content and the materials with very small energy band gap possess the highest absorption coefficient. The investigation of the linear and nonlinear optical susceptibilities of GaAs1−xBix shows a strong band gap reduction as commonly found experimentally. 相似文献
5.
Jian-Ping Zou Sheng-Lian LuoXing-Hua Tang Ming-Jun LiAi-Qin Zhang Qiang Peng Guo-Cong Guo 《Journal of Alloys and Compounds》2011,509(2):221-225
A new framework compound, [Hg4As2](InBr3.5As0.5) (1), has been prepared by the solid-state reaction of Hg2Br2 with elemental In and As at 450 °C. Compound 1 crystallizes in the space group P63/mmc of the Hexagonal system with two formula units in a cell: a = b = 7.7408(6) Å, c = 12.5350(19) Å, V = 650.47(12) Å3. The crystal structure of 1 features a novel 3D framework, [Hg4As2]2+ with tridymite topology. The optical properties were investigated in terms of the diffuse reflectance and infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is semiconductor, and the optical absorption is mainly originated from the charge transitions from Br-4p and As-4p states to Hg-6s and In-5p states. 相似文献
6.
The experimental study of the optical properties of CeNi5, CeNi4Cu and CeNi4Al compounds was carried out in the 0.083-5.64 eV energy range using the ellipsometry method. The optical constants, dielectric functions and electronic parameters (plasma and relaxation frequencies) were determined. The energy dependencies of the optical interband conductivities are discussed by using the available information on the electronic band structure of these compounds. In the ternary alloys the optical spectra show the presence of peculiarities related to effect of Cu or Al substitution at Ni sites. 相似文献
7.
Yongkwan Dong Chinmoy Ranjan Francis J. DiSalvo 《Journal of Alloys and Compounds》2007,430(1-2):54-59
Two polymorphs (I and II) of Ba3Sn2P4 have been found in the same preparative batch. Both compounds crystallize in the centrosymmetric monoclinic space group P21/c (#14, a = 7.8669(2) Å, b = 19.2378(5) Å, c = 7.8472(2) Å, β = 112.77(1)°, V = 1095.06(5) Å3, Z = 4, and R/wR = 0.0303/0.0710 for I; a = 7.8771(3) Å, b = 19.4099(7) Å, c = 7.7040(3) Å, β = 112.44(1)°, V = 1088.67(7) Å3, Z = 4, and R/wR = 0.0224/0.0415 for II). Both structures consist of one-dimensional chains separated by Ba2+ cations. The isolated chain consists of condensed ethane-like [Sn2P6] units. In polymorphs I and II, the condensation and connectivity of the [Sn2P6] units are quite different. While [Sn2P6] units form four- and six-membered rings in I, they form the five-membered rings in II. The electronic structure calculations indicate that semiconducting behavior is expected for both compounds. 相似文献
8.
Altaf Hussain Sitaram AryalPaul Rulis M. Arshad ChoudhryJun Chen W.Y. Ching 《Journal of Alloys and Compounds》2011,509(17):5230-5237
The electronic structure and optical properties of the Ni3Al intermetallic alloy are studied by the first-principles orthogonalized linear combination of atomic orbitals method. Disordered models at different temperatures were constructed using molecular dynamics and the Vienna ab initio simulation package. The average charge transfer from Al to Ni increases steadily with temperature until the liquid phase is reached. The localization index shows the presence of relatively localized states even above the Fermi level in the disordered models. The calculated optical conductivity of the ordered phase is rich in structures and in reasonable agreement with the experimental data. The spectra of the disordered Ni3Al models show a single broadened peak at 4.96 eV in the 0 K model which shifts towards 6.62 eV at 1400 K and then down to 5.83 eV in the liquid phase. Other results on the band structure and density of states are also discussed. 相似文献
9.
A. Kowalczyk M. Falkowski V.H. Tran M. Pugaczowa-Michalska 《Journal of Alloys and Compounds》2007,440(1-2):13-17
The studies of the thermoelectric power and band structure calculations for CeNi4Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi4Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μeff = 0.52μB/f.u. and the paramagnetic Curie temperature θP = −2 K. This effective paramagnetic moment is lower than the free Ce3+ value. The obtained values for the f occupancy nf and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi4Si is characterized by γ = 16 mJ mol−1 K−2 and θD = 335 K. 相似文献
10.
Based on the first-principles density-functional theory, the electronic structures and optical properties of monoclinic HfO2 and Ti-doped m-HfO2 are comparatively investigated. The calculated lattice parameters of m-HfO2 are in good agreement with the experimental values and the previous works, and the incorporation of Ti into HfO2 induces a decrease in the lattice parameters. Electronic structures of m-HfO2 and Ti-doped HfO2 are studied through the densities of states (DOS) and band structures. The results indicate that the Ti substitution of Hf sites modifies the conduction band structure of HfO2, which leads to a reduction of the band gap of HfO2. The complex dielectric function and refractive index are calculated and the peak position distributions of imaginary parts of the complex dielectric function have been explained. The calculated optical properties are consistent with the experimental measurements for m-HfO2. 相似文献
11.
The crystal structure of intermetallic compound Gd6Cr4Al43 has been investigated by means of X-ray diffraction data (Ho6Mo4Al43 structure type, space group P63/mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å).
SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at TN1 = 19.0(1) K and TN2 = 6.8(1) K, respectively. 相似文献
12.
H. Ihou-Mouko C. MercierJ. Tobola G. PontH. Scherrer 《Journal of Alloys and Compounds》2011,509(23):6503-6508
Mg2Si:Gax and Mg2Si0.6Ge0.4:Gax (x = 0.4% and 0.8%) solid solutions have been synthesized by direct melting in tantalum crucibles and hot pressing. The effect of Ga doping on the thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K. All samples exhibit a p-type conductivity evidenced by positive sign of both thermopower and Hall coefficient in the investigated temperatures. The maximum value of the dimensionless figure of merit ZT was reached for the Mg2Si0.6Ge0.4:Ga(0.8%) compound at 625 K (ZT ∼ 0.36). The p-type character of thermoelectric behaviours of Ga-doped Mg2Si and Mg2Si0.6Ge0.4 compounds well corroborates with the results of electronic structure calculations performed by the Korringa-Kohn-Rostoker method and the coherent potential approximation (KKR-CPA), since Ga diluted in Mg2Si and Mg2Si0.6Ge0.4 (on Si/Ge site) behaves as hole donor due to the Fermi level shifted to the valence band edge. The onset of large peak of DOS from Ga impurity at the valence band edge, well corroborates with high Seebeck coefficient measured in Ga-doped samples. 相似文献
13.
Xiuai Lu Zhenyu You Jianfu Li Zhaojie Zhu Guohua Jia Baichang Wu Chaoyang Tu 《Journal of Alloys and Compounds》2008,458(1-2):462-466
The polarized absorption and emission spectra have been measured for the Tm3+ doped NaY(MoO4)2 crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters (t = 2, 4, 6) are 11.67 ×10−20, 2.21 × 10−20, 1.74 × 10−20 cm2, respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm3+ doped laser crystals, Tm3+:NaY(MoO4)2 crystal has potential as a promising laser crystal. 相似文献
14.
CoAl2O4 nanocrystals were synthesized by sol-gel method using citric acid as a chelating agent at low temperature. The as-synthesized samples were characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that CoAl2O4 spinel is the only crystalline phase with a size of 10-30 nm in the temperature range 500-1000 °C. The temperature dependence of the distribution of Al3+ and Co2+ ions in the octahedral and tetrahedral sites in nanocrystals was investigated by X-ray photoelectron spectroscopy (XPS). It is observed that the inversion parameter decreases with increasing annealing temperature. Analysis of the absorption properties indicates that Co2+ ions are located in the tetrahedral sites as well as in the octahedral sites in the CoAl2O4 nanocrystals. The origin of the green color (300-500 nm absorption band) should be due to the octahedrally coordinated Co2+ ions. 相似文献
15.
Rui-Shuo ZhangYong Liu Qian GaoFan Teng Chen-Lu Song Wei WangGao-Rong Han 《Journal of Alloys and Compounds》2011,509(37):9178-9182
We present a comparative study on the electronic and optical properties of Nb- and F- doped anatase TiO2 by first-principles calculations based on the density functional theory (DFT). Although both TiO2:Nb and TiO2:F have a similar band structure, the effective mass of TiO2:F is larger than that of TiO2:Nb, and the carriers density in the former is lower than that in the latter, indicating that TiO2:Nb has better electronic conductivity than TiO2:F. The interaction between photons and electrons in TiO2:F is much stronger than that in TiO2:Nb, resulting in increased photon absorption and reduced transmittance, especially in the visible and near-infrared regions. The results demonstrate that TiO2:F is not suitable for transparent conductive oxide applications. 相似文献
16.
S. SaipriyaR. Singh 《Journal of Alloys and Compounds》2011,509(38):9318-9321
Multilayers (ML) of [SnO2/Mn]n were deposited by RF-magnetron sputtering on quartz substrates at room temperature using metal targets. The XRD pattern and the XRR show amorphous and discontinuous nature of ML respectively. The transmittance (at 550 nm) as well as the estimated optical band gap (Eg) decreases with the increase in the number of bilayers. The present study shows that the optical properties of the present ML can be tuned by changing the n value. 相似文献
17.
Andrew D. GledhillDongsheng Li Thomas MrozLee M. Goldman Nitin P. Padture 《Acta Materialia》2012,60(4):1570-1575
In response to a need for improving the mechanical properties of optically transparent ceramics, the nanocomposites approach is used to strengthen transparent magnesium-aluminate spinel with Si3N4 nanodispersoids. The as-processed nanocomposites are found to be >70% transparent in the critical infrared wavelength range of 3-4.5 μm. Mie scattering combined with absorption by the Si3N4 nanodispersoids explains quantitatively the IR transmission behavior of these nanocomposites. The nanocomposites are also found to be transparent in the visible region. Upon heat treatment (1000 °C for 4 h in air), the optical properties of the nanocomposites remain unchanged. However, the heat treatment results in a 29% increase in the average strength, accompanied by almost doubling of the Weibull modulus, and an 85% increase in the indentation toughness. The improvements in mechanical properties after the heat treatment in these nanocomposites are explained qualitatively, based on generally accepted arguments involving surface-oxidation-induced surface compression and flaw-healing. While further work is needed to fully understand and exploit these effects, this first report on transparent nanocomposites could have broad implications for the creation of mechanically robust, transparent ceramics of the future. 相似文献
18.
WO3-doped zinc titanate ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. The effects of WO3 additions on the phase structure and phase transitions of zinc titanate ceramics were investigated by high-temperature X-ray diffractometry (HTXRD) and transmission electron microscopy (TEM). The results showed that the major phase of zinc titanate ceramics transformed from zinc orthotitanate phase to zinc metatitanate phase with the amounts of WO3 additions increasing. Small WO3 (<1.00 mass%) addition accelerated the transition of ZnTiO3 to Zn2TiO4, while excessive WO3 addition restrained the transition. HTXRD showed that WO3 enhanced the stability of Zn2Ti3O8 and weakened the stability of ZnTiO3. A precipitate within the Zn2TiO4 matrix was observed. Viewed along the orientation of Zn2TiO4, the precipitate was found to have a rectangular shape and to be nanometer level in size; its composition was concluded to be Zn2Ti3O8. The dielectric properties of WO3-doped zinc titanate ceramics were measured at different frequencies. The results showed the decreasing tendency with the increasing measuring frequencies for both the dielectric constants and the loss tangents, and there existed maximum values when the amount of WO3 was 0.50 mass%. 相似文献
19.
采用基于密度泛函理论(DFT)框架下广义梯度近似(GGA)的PBE平面波超软赝势方法,计算Cu2ZnSnS4(CZTS)和Cu2ZnSnSe4(CZTSe)的电子结构和光学特性。计算并系统对比分析CZTS和CZTSe的态密度、吸收系数、复介电函数、复折射率、反射率、复电导率和能量损失函数随光子能量的变化关系。结果表明,锌黄锡矿型CZTS和CZTSe都是直接带隙半导体材料。CZTS和CZTSe的态密度和光学特性的曲线非常相似,但CZTS的禁带宽度比CZTSe的偏大,导致CZTS的各个光学特性曲线相对于CZTSe的略微向高能方向移动。 相似文献
20.
R. KumaravelK. Ramamurthi 《Journal of Alloys and Compounds》2011,509(12):4390-4393
Preparation of highly conducting and transparent In-doped Cd2SnO4 thin film by spray pyrolysis method at a substrate temperature of 525 °C is reported. In-doping concentration is varied between 1 and 5 wt.%. The effect of In-doping on structural, optical and electrical properties was investigated using different techniques such as X-ray diffraction, atomic force microscopy, optical transmittance and Hall measurement. X-ray diffraction studies revealed that the films are polycrystalline with cubic crystal structure. The undoped and In-doped Cd2SnO4 films exhibit excellent optical transparency. The average optical transmittance is ∼87% in the visible range for 3 wt.% In-doping. Further In-doping widens the optical band gap from 2.98 ± 0.1 eV to 3.04 ± 0.1 eV. A minimum resistivity of 1.76 ± 0.2 × 10−3 Ω cm and maximum carrier concentration of 9.812 ± 0.4 × 1019 cm−3 have been achieved for 1 wt.% In-doping in Cd2SnO4 thin films. 相似文献