共查询到20条相似文献,搜索用时 15 毫秒
1.
Qi-Jun Liu Zheng-Tang LiuJi-Chao Chen Li-Ping FengHao Tian 《Physica B: Condensed Matter》2011,406(18):3377-3382
We calculated the structural parameters, elastic, mechanical, electronic and optical properties of 3R- and 2H-CuGaO2 using the first-principles density-functional theory. The results show that the structural parameters of two phases are in good agreement with previous theoretical and experimental data. Two phases are mechanically stable, behave in ductile manner and have indirect band gap. The analyses of electronic structures and charge densities of two phases show mainly covalent nature in Cu-O bonds and coexistence of both ionic and covalent nature in Ga-O bonds. The optical properties are obtained and discussed, including the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and complex conductivity function, which provide useful information for the future applications of CuGaO2. 相似文献
2.
Meili GuoJiulin Du 《Physica B: Condensed Matter》2012,407(6):1003-1007
We perform first-principles calculations to investigate the band structure, density of states, optical absorption, and the imaginary part of dielectric function of Cu, Ag, and Au-doped anatase TiO2 in 72 atoms systems. The electronic structure results show that the Cu incorporation can lead to the enhancement of d states near the uppermost of valence band, while the Ag and Au doping cause some new electronic states in band gap of TiO2. Meanwhile, it is found that the visible optical absorptions of Cu, Ag, and Au-doped TiO2, are observed by analyzing the results of optical properties, which locate in the region of 400-1000 nm. The absorption band edges of Cu, Ag, and Au-doped TiO2 shift to the long wavelength region compared with the pure TiO2. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Cu, Ag, and Au-doped TiO2. Our results show that the visible light response of TiO2 can be modulated by substitutional doping of Cu, Ag, and Au. 相似文献
3.
Bo ZhuChun-Mei Liu Ming-Bang LvXiang-Rong Chen Jun Zhu Guang-Fu Ji 《Physica B: Condensed Matter》2011,406(18):3508-3513
We investigate the structural, phase transition and elastic properties of SnO2 in the rutile-type, pyrite-type, ZrO2-type and cotunnite-type phases by the plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are well consistent with the available experimental and other theoretical data. Also, we find that the rutile→pyrite, pyrite→ZrO2 and ZrO2→cotunnite phase transition occur at 12.9, 59.1 and 111.1 GPa, which are in better agreement with the experimental results than those of Gracia et al. (2007). Moreover, we obtain the pressure dependences of elastic constants for the four structures. 相似文献
4.
The plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) is used to investigate the doping effect of N substituting for O in cubic SrHfO3. The calculated results show that the reaction from pure elements to final compounds is favorable and the final compounds are energetically stable. Electronic structure analysis shows the band gaps narrowing with the increase of N concentration due to the presence of the impurity state of N 2p on the top of the valence band and the acceptor energy levels above the Fermi energy, which may be responsible for the red-shift. Besides, the optical absorption edge has been gradually red shifted with increasing N concentration. 相似文献
5.
采用基于密度泛函理论的广义梯度近似方法研究了稳态六方petrov原子序列结构Ge2Sb2Te5的结构、电子和光学性质。计算所得的平衡态晶格参数与实验数据和先前的理论结果吻合很好。基态的能带结构和态密度表明了稳态六方petrov原子序列结构的Ge2Sb2Te5持有金属性。从压强影响下体积的变化趋势发现稳态六方Ge2Sb2Te5在17 GPa和34 GPa 出现不稳定,暗示在此压强下的相变发生,这与2009年Krbal等人的实验结果相吻合。同时,还系统地研究了稳态六方petrov原子序列结构的Ge2Sb2Te5高压下的光学性质,得到了高压下介电函数、吸收率、光反射率、折射率、消光系数和电子能量损失谱在20 eV内的变化情况。 相似文献
6.
Y2O3 transparent ceramics with different Nd concentration (0.1-7.0at%) were fabricated using ZrO2 as additive. All the samples exhibit high transparency over a broad spectral region. The elements (Y, O and Nd) are uniformly distributed in the ceramic body, and the average grain size increases with Nd content. Based on the absorption spectrum, the Judd-Ofelt intensity parameters are calculated (Ω2=4.364×10−20 cm2, Ω4=3.609×10−20 cm2 and Ω6=2.919×10−20 cm2). The absorption coefficients increase linearly with Nd3+ doping concentration. The absorption cross-section at 804 nm and stimulated emission cross-section at 1078 nm are calculated to be 1.54×10−20 and 7.24×10−20 cm2, respectively. All the emission bands exhibit the highest emission intensities with 1.0at% Nd3+ ion content, while the lifetime decreases dramatically from 321.5 μs (0.1at% Nd) to 17.9 μs (7.0at% Nd). According to the emission spectra and measured lifetime, the optimum doping concentration of Nd3+ ion in Y2O3 transparent ceramic might be around 1.0at%. 相似文献
7.
Thin Er3+, Yb3+ co-doped Y2O3 films were grown on (1 0 0) YAG substrates by pulsed laser deposition. Ceramic targets having different active ion concentration were used for ablation. The influence of the rare-earth content and oxygen pressure applied during the deposition on the structural, morphological and optical properties of the films were investigated. The films deposited at the lower pressure, 1 Pa, and at 1/10 Er to Yb doping ratio are highly textured along the (1 1 1) direction of the Y2O3 cubic phase. In addition to the crystalline structure, these films possess smoother surface compared to those prepared at the higher pressure, 10 Pa. All other films are polycrystalline, consisting of cubic and monoclinic phases of Y2O3. The rougher surface of the films produced at the higher-pressure leads to higher scattering losses and different behavior of the reflectivity spectra. Optical anisotropy in the films of less than 0.004 was measured regardless of the monoclinic structure obtained. Waveguide losses of about 1 dB/cm at 633 nm were obtained for the films produced at the lower oxygen pressure. 相似文献
8.
First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga
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The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable. 相似文献
9.
CdS doped TiO2 thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO2 structure. The microstructure parameters of the films such as crystallite size (Dν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of Egopt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO2. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO2, although they have lower band gap. The CdS doped TiO2 could have a better impact on the decomposing of organic wastes. 相似文献
10.
Based on the density functional pseudopotential method, the electronic structures and the optical properties of CdI2 doped with Cu are investigated in detail. The calculation results indicate that the defect of Cu(Cd) exists steadily with a certain solubility. For the Cu doped CdI2, the new highly localized impurity bands induced by Cu 3d states lie just across the Fermi energy at the top of the valence band. The doping of Cu induces reduction of band gap of CdI2; red shifts are revealed in both the imaginary part of dielectric function and the absorption spectra corresponding to the change in band gaps. Moreover, the study of the reflection spectrum and the loss function shows that the doped Cu is responsible for the increased reflection peak intensity and the red shift of the plasma resonant frequency of CdI2. 相似文献
11.
Different stable geometric configurations of Ge doped amorphous SiO2 (a-SiO2) system, originating from one, two, or three Si atoms in various places of the a-SiO2 substituted by Ge atoms randomly have been investigated using interatomic potentials in this work. The most stable structures have been identified and corresponding evolutional rules obtained. The structural growth pattern for Ge-doped a-SiO2 system is that Ge atoms tend to spread far away from each other and keep away from the center. Furthermore, the thermodynamic properties including speci?c heat, Debye temperature, vibrational entropy, and so on are calculated from the structure with 16 Si atoms of the constructed a-SiO2 cell replaced by Ge atoms and with the biggest Ge-Ge distance. It can be seen that entropy of Ge doped system with larger specific heat is higher than that of the pure system with smaller specific heat. At last, optical properties including optical absorption spectrum and electron energy loss function of nGe-doped a-SiO2 (n=0-3, 8) system is also obtained. 相似文献
12.
采用平面波赝势密度泛函理论方法对0—60 GPa静水压下BC5 六角晶系P3m1和四方晶系I4m2结构的平衡态晶格常数、弹性常数、各向异性以及泊松比与Cauchy扰动进行了研究. 研究结果表明, BC5的两种结构在高压下是稳定的, 且不可压缩性随着压强的增加而增大. 另外, 对其电子结构也进行了计算, 计算结果表明, BC5存在一个较宽的带隙, 两种原子间有较强的共价杂化, 材料的性质主要由B的2p1和C的2p2态电子共同决定. 压强对材料带隙和费米能级附近的态密度几乎没有影响, 只引起微小的漂移, 可推断其很好的高压稳定性. 相似文献
13.
A non-linear variation of bandgap energy with Co doping is observed in sputter deposited Co-doped TiO2 thin films. This peculiar behavior is explained on the basis of mechanical stress in the films together with spin polarization due to s,p-d exchange interaction between the localized Co 3d electrons and delocalized electrons. Quantitative analyses of mechanical stress and grain boundary barrier potential due to spin polarization are performed from the below bandgap absorption tail. Furthermore, anomalous variations in both the refractive indices and extinction coefficients with Co doping are noted and are explained on the basis of ab-initio calculations based on density functional theory. 相似文献
14.
M.A. HelalA.K.M.A. Islam 《Physica B: Condensed Matter》2011,406(24):4564-4568
The elastic, electronic, and optical properties of MNNi3 (M=Zn, Sn, and Cu) have been calculated using the plane-wave ultrasoft pseudopotential technique, which is based on the first-principle density functional theory (DFT) with generalized gradient approximation (GGA). The optimized lattice parameters, independent elastic constants (C11, C12, and C44), bulk modulus B, compressibility K, shear modulus G, and Poisson's ratio υ, as well as the band structures, total and atom projected densities of states and finally the optical properties of MNNi3 have been evaluated and discussed. The electronic band structures of the two hypothetical compounds show metallic behavior just like the superconducting ZnNNi3. Using band structures, the origin of features that appear in different optical properties of all the three compounds has been discussed. The large reflectivity of the predicted compounds in the low energy region might be useful in good candidate materials for coating to avoid solar heating. 相似文献
15.
Ziyu Hu 《Phase Transitions》2015,88(7):726-734
Using first-principles methods, we systematically investigate the electronic properties and atomic mechanism of the monolayer MoS2/WS2 homo-junction structure, which contains different phase structures, either the semiconducting hexagonal (H) structure or metallic trigonal (T) structure. Through tuning the size of the lateral homo-junction structure of either MoS2 or WS2, it can produce different boundaries which induce different phase transferred styles. More interestingly, the electronic structures of homo-junction structures can also be tuned by changing the size of the armchair and zigzag shapes of nanoribbons. The homo-junction structure of either MoS2 or WS2 exhibits alterable band structure and band edge position with the changing of the size. The strong dependence of the band offset on the sizes of the homo-junction monolayer also implicates a possible way of patterning quantum structures with size engineering. 相似文献
16.
M.S. IslamA.K.M.A. Islam 《Physica B: Condensed Matter》2011,406(2):275-279
We propose a new layered-ternary Ta4SiC3 with two different stacking sequences (α- and β-phases) of the metal atoms along c axis and study their structural stability. The mechanical, electronic and optical properties are then calculated and compared with those of other compounds M4AX3 (M=V, Nb, Ta; A=Al, Si and X=C). The predicted compound in the α-phase is found to possess higher bulk modulus than these compounds. The independent elastic constants of the two phases are also evaluated and the results discussed. The electronic band structures for α- and β-Ta4SiC3 show metallic conductivity. Ta 5d electrons are mainly contributing to the total density of states (DOS). We see that the hybridization peak of Ta 5d and C 2p lies lower in energy and the Ta 5d-C 2p bond is stronger than Ta 5d-Si 3p bond. Further an analysis of the different optical properties shows the compound to possess improved behavior compared to similar types of compounds. 相似文献
17.
Belt-like VO2(M) with a rectangular cross section: A new route to prepare, the phase transition and the optical switching properties 总被引:1,自引:0,他引:1
Yifu ZhangMeijuan Fan Fei NiuWeibing Wu Chi Huang Xinghai Liu Houbin LiXin Liu 《Current Applied Physics》2012,12(3):875-879
Belt-like VO2(M) with a rectangular cross section was first synthesized by the irreversible transformation of VO2(A) at the elevated temperatures under the inert atmosphere to the best of our knowledge. The as-obtained samples were characterized by a combination of techniques including XRD, SEM and TEM. The processes of converting VO2(A) to VO2(M) were briefly discussed. The as-obtained VO2(M) has belt-like morphology with a rectangular cross section with typical lengths up to several tens of micrometers, widths ranging from tens of nanometers to several micrometers, and thicknesses about 60-150 nm. The morphology and size of the VO2(M) were dependent on that of the precursor VO2(A). The phase transition properties of VO2(M) were investigated by DSC, indicating that it exhibited a strong phase transition at 67.9 °C in the heating cycle and 61.1 °C in the cooling cycle. Furthermore, the optical switching property of VO2(M) was studied by the variable-temperature infrared spectra, and it was found that the as-obtained VO2(M) could be used as the optical switch. 相似文献
18.
The concentration-dependent electronic structures and optical properties of B-doped anatase TiO2 have been calculated using the density functional theory. The calculated results indicate that the electronic structures of B-doped TiO2 have changed compared with those of pure TiO2, which is mainly due to the new midgap states induced by B doping. As to the optical properties, we calculate the imaginary part of dielectric function ε2(ω) and optical absorption spectra of pure and B-doped TiO2. Two transitions E1 and E2 emerged after B doping. The intensity of absorption is enhanced by B doping both in the UV and visible regions. According to the results of imaginary part of dielectric function ε2(ω) and DOS, it can be concluded that the two optical transitions correspond to the transitions from the O 2p states in the top of valence band to the midgap states and from the midgap states to the Ti 3d states in the bottom of conduction band, respectively. These results have important implications for the further development of photocatalytic materials. 相似文献
19.
Pure and WO3 doped CeO2-PbO-B2O3 glasses are prepared by the melt-quench technique. The structural and optical analyses of glasses are carried out by XRD, FTIR, density and UV-vis spectroscopic measurement techniques. FTIR analysis indicates the transformation of structural units of BO3 into BO4 with W-O-W vibration and the presence of WO4 and WO6 units observed with increase in WO3 contents. Decrease in band gap for CeO2-PbO-B2O3 glasses from 2.89 to 2.30 eV and for WO3 doped glasses from 2.89 to 1.95 eV has been observed and discussed. This decrease in band gap with WO3 doping approaches to semiconductor behavior. It shows that the presence of WO3 in the glass samples causes more compaction of the borate network due to the formation of BO4 groups and the presence of WO4 and WO6 groups, which result in a decrease in the optical band gap energy and increase in the density. 相似文献
20.
In this work, we report a quite different conclusion from Tian et al. [Phys. Rev. B 78 (2008) 235431]. It is proved that β-C3N2 is the only phase under high pressure, and α-C3N2 does not exist. β-C3N2 is a covalent crystal composed of strong CC and CN covalent bonds. Band gap of β-C3N2 increases with pressure. The width of antibonding state, shown in partial density of states (PDOS), keeps about 5 eV with rising pressures, which brings stable CN or CC covalent bonds. At sufficiently low temperatures, heat capacity (Cv) is proportional to T3; and at intermediate temperatures, Cv is governed by the details of vibrations of the atoms; finally, Cv reaches to β-C3N2's Dulong–Pettit limit (about 120 J/mol K). Though thermal expansion coefficient (α) increases with temperature, α is less than 1×10−5 K−1. Elastic constants rise with pressure, but shear moduli is quite steady which increases just a little with pressures. 相似文献