X-Ray Spectra and Electronic Structure of 3C SiC and BN Based Solid Solutions

The local coherent potential approximation is used in the framework of multiple-scattering theory to calculate the electronic energy structure of solid solutions of silicon carbide Si_1-xCR_x and boron nitride BN_1-xR_x and B_1-xNR_x (x = 0-0.75, R = C, Al, Ti) in a diamond-like modification. The total and partial densities of states are calculated for each atom in the solid solutions. The crystal potential is evaluated in an MT approximation. The lattice parameter is determined by Vegard's rule. The electronic energy structures of the solid solutions are compared with each other and with binary analogs in the framework of one approximation. The calculated partial densities of states are compared with the experimental X-ray spectra of silicon in the compounds. The calculation of the partial charges of atoms at the top of the valence band showed that the charge transfer (0.35 e) from boron to nitrogen in binary 3C BN changes sign in B_0.75NC_0.25. In the latter system, nitrogen donates 0.19 e to boron, and carbon acts as a donor for the electronic configurations of boron and nitrogen. An electronic structure analysis of the solid solutions indicates that the quasicore resonance states inherent in the binary compounds are delocalized, probably because of the weakening of chemical binding in the solid solutions.     

X-ray spectra and electronic structure of boron nitride in different crystallographic modifications

The electronic energy structure of boron nitride with ZnS (c-BN) and wurtzite (w-BN) type crystal lattices is calculated by the local coherent potential (LCPA) method in a multiple scattering approximation. The local partial 2p states of boron with c-BN and w-BN are compared with the boron K emission spectra in the corresponding compounds. Fine structure is first obtained in the region of the top of the valence band. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1083–1087, November–December, 1998.     

X-ray spectra and electronic structure of several ternary chalcogenides and their solid solutions

The electronic energy structure of substitution solid solutions CuGa(S_xSe_1−x)₂ is studied within wide limits of sulfur concentration x in the onion sublattice. The SK absorption spectrum is calculated for CuGaS₂ in a high-order multiple scattering approximation using the FEFF7 program. For all concentrations x, partial densities of states are calculated in a full multiple scattering approximation by the local coherent potential method. The calculation schemes for the filled and vacant states are employed, which differ in a choice of the crystalline potential. The effect of a vacancy on the SK level on the density of the free Sp states is considered. The theoretical K absorption spectra and densities of states of CuGaS₂ are compared with the experimental X-ray and X-ray photoelectron spectra. The calculated curves are in good agreement with the experiment. It is established that the densities of the S and Se p states change smoothly with varying concentration of anions. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1076–1082, November–December, 1998.     

X-ray spectra and features of the electron energy structure of TaC, TaN, HfC, TaC0.5N0.5, and Hf0.5Ta0.5C

The electron energy structure of titanium and hafnium carbide, titanium and solid solutions of TaC_0.5N_0.5 and Hf_0.5Ta_0.5C nitride is investigated experimentally (by X-ray and X-ray photoelectron spectroscopy) and theoretically (based on the quantum mechanical calculations in a full multiple scattering approximation, by the program FEFF8 with a self-consistent semirelativistic potential). A good accordance between the calculated curves of the densities of electronic states and the corresponding experimental curves is obtained. The chemical bond features in the investigated compounds and solutions are revealed.     

Dependence of the forbidden gap on sulfur concentration for znsxse1-x solid solutions

Substitution solid solutions A_IIB_VI demonstrate a nonlinear dependence of the forbidden gap E_g on concentration (optical deflection). The magnitude of the deflection depends on both chemical and structural factors. Atomic ordering in solution may also affect this value. Ab initio densities of states are calculated for the cubic modification of ZnS_xSe_1-x solid solutions (x = 0.0, 0.17, 0.33, 0.50, 0.67, 0.83, 1.0) in a virtual crystal approximation using the cluster version of the local coherent potential method in terms of full multiscattering theory. The chemical disordering effect was studied for a 50% solution with a sphalerite structure. The bond discrepancy effects were modeled for the 50% solution using ternary structures: chalcopyrite (CuFeS₂ type) and ordinary tetragonal structure (CuAul type). The calculated optical deflection parameters are in good agreement with the experimental values and with the data obtained by other authors. The calculated densities of states also agree well with the experimental X-ray and X-ray photoelectron data for the terminal compounds ZnS and ZnSe. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 498-504, May–June, 2000.     

Structural and electronic properties of aln and bn wide-gap semiconductors and their B<Subscript>x</Subscript>Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N solid solutions

The structural and electronic properties of B_xAl_1−x N solid solutions (x = 0.25, 0.5, 0.75) were examined by calculating the electronic energy structure by the local coherent potential method within the framework of multiple scattering theory. The charge is transferred from aluminum to nitrogen atoms and increases with the content of boron atoms. The concentration dependences of the structural and electronic properties of these solutions are discussed. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 5, pp. 822–829, September–October, 2005.     

Electronic structure of carbon nanotubes with an impurity point defect

A method for calculating the electronic structure of point defects in nanotubes is developed on the basis of the linear augmented cylindrical wave (LACW) method. The Green function of a defect nanotube is calculated using the Dyson matrix equation. The consideration is carried out in terms of the local density functional theory and the muffin-tin approximation for the electronic potential. Local densities of state are calculated for boron and nitrogen dopants in metal, semimetal, and semiconductor and chiral and nonchiral nanotubes. An increased density of states at the Fermi level is the most significant effect of boron and nitrogen dopants in metal nanotubes. In all semiconductor nanotubes, localized boron states close the optical band-gap. The effect of nitrogen atoms is restricted to a small rise in local densities of state at the Fermi level.     

Co-cation conduction in solid electrolytes based on AAlO2 (A = Li, Na)

Regions of the formation of tetragonal solid solutions with the γ-LiAlO₂ structure and the co-cation conduction are studied in the systems 0.9Na_1-xLi_xAlO₂-0.1EO₂ (E = Ti, Ge, Si) and 0.8Na_1-xLi_xAlO₂-0.2TiO₂. The single-phase regions of solid electrolytes narrows down with decreasing size of cations of a rigid lattice. No polyalkaline effect exists in the above systems. In the single-phase region of solid solutions, variations in the conductivity is caused largely by variations in the partial conductivity of the more mobile sodium cation.     

On the Determination of Partial Molar Volumes,Partial Molar Refractions,Mean Electronic Polarizabilities and Effective Molecular Radii from Dilute Multi-component Data alone using Response Surface Models

A quaternary system consisting of three solutes, namely ethanol, diethylene glycol (DEG) and triethylene glycol (TEG) in benzene at 298.15 K and 1.0125 × 10⁵ Pa was studied. An experimental design in the range of concentration 0.006 < x _solute−i < 0.023 was explored, optimizing the metric distance among the solutes to avoid clustering. On-line simultaneous experimental measurements using a densitometer and a refractometer were utilized to measure bulk solution density and bulk refractive index, respectively. Response surface models describing the total molar volume and total molar refraction were employed to determine the partial molar volumes and the partial molar refractions of each solute from the dilute multi-component data alone. Neither densities nor refractive indices of any of the pure components were used and no binary information was required for the analysis. Definitions for the mean electronic polarizability and the effective molecular radius of a solute based on the partial molar refraction were introduced. Subsequently, the mean electronic polarizabilities and the effective molecular radii for each solute in multi-component solutions, as well as the solvent were determined. The results obtained for the partial molar volumes, partial molar refractions, electronic polarizabilities and the effective molecular radii were in good agreement with those obtained from independent binary experiments as well as those from literature binary data.     

AgGa(S1-xSex)2固溶体的电子结构和光学性质

采用基于赝势平面波基组的密度泛函理论方法, 对一系列具有黄铜矿结构的AgGa(S_1-xSe_x)₂固溶体的构型、电子结构、线性和二阶非线性光学性质进行了系统研究. 结果表明, 各固溶体具有类似的能带结构, 体系带隙随x值增加而逐渐减小. 当所引入的Hartree-Fock交换项贡献为22.56%时, 对应的杂化PBE泛函得到的带隙值与实验结果相近. 固溶体的各种光学性质, 包括折射率、双折射率、反射率、吸收系数和二阶倍频系数等均随着组成的改变呈现出有规律的变化趋势, 变化范围介于AgGaS₂和AgGaSe₂二者之间. 因此, 利用固溶体光学性质的变化规律, 可从中寻找出具有特定光学性能的晶体材料.     

A First‐Principles Investigation on Microscopic Atom Distribution and Configuration‐Averaged Properties in Cd1−xZnxS Solid Solutions

The structural, energetic, and electronic properties of zincblende and wurtzite phase Cd_1?xZn_xS (0≤x≤1) solid solutions were investigated by first‐principles calculations. It was revealed that the trend of atom distribution in configurations with the same x value can be quantitatively characterized by the average length of the Zn?S bonds. The origin of this trend was attributed to the strong interaction of the Zn?S bonds, which acted against the aggregation of Zn atoms in this solid solution. By using a configuration‐averaged method, structural and energetic properties were estimated as a function of Zn content at the level of the generalized gradient approximation, whereas electronic properties were corrected by using a hybrid functional. Phase diagrams of both solid solutions were established. An optimal x value of approximately 0.5 for photocatalytic hydrogen production was determined by taking both the band edges and band gaps into consideration; this conclusion was supported by the results of a variety of experiments.     

Low temperature heat capacities of mechanically alloyed La-doped PbWO4 system

Heat capacity measurements were carried out on Pb_1-xLa_xWO_4+x/2 (x=0.2) and Pb_1-xLa_2x/3WO₄ (x=0.2, 0.5) solid solutions prepared by sintering and mechanical alloying (MA) methods. For all the solid solutions, sintered samples showed slightly larger heat capacity around 100 K in comparison with MA samples, which was presumably caused by the excitation of mobile oxide ion motion. For sintered scheelite-type structured PbWO₄s, high-temperature synthesis introduced oxide ion interstitials even for the Pb_1-xLa_2x/3WO₄ system, which resulted in the excess heat capacity at low temperature for excitation. On the other hand, for the samples prepared by room-temperature MA technique, oxide ion seemed to occupy the regular sites rather than interstitial ones and excess heat capacities were not observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ru掺杂SnO2半导体固溶体的电子结构研究

运用基于密度泛函理论的第一性原理方法,建立了SnO₂以及不同比例Ru掺杂的SnO₂超胞模型,在对其进行几何优化后计算了Sn_1-xRu_xO₂(x=0,1/16,1/12,1/8,1/6,1/4,1/2)半导体的电子结构,并讨论了其晶格参数、电荷密度、能带结构和态密度(包括分态密度)等性质。结果表明,掺杂后,晶格参数随掺杂量的增加线性减小,与实验值的偏差在4%以内;掺杂后,在费米能级处可以提供更多的填充电子,使得电子跃迁至导带更容易,固溶体的导电性增强。为Sn_1-xRu_xO₂固溶体电极材料的发展和应用提供了理论基础。     

Ru掺杂SnO2半导体固溶体的电子结构研究

运用基于密度泛函理论的第一性原理方法,建立了SnO₂以及不同比例Ru掺杂的SnO₂超胞模型,在对其进行几何优化后计算了Sn_1-xRu_xO₂(x=0,1/16,1/12,1/8,1/6,1/4,1/2)半导体的电子结构,并讨论了其晶格参数、电荷密度、能带结构和态密度(包括分态密度)等性质。结果表明,掺杂后,晶格参数随掺杂量的增加线性减小,与实验值的偏差在4%以内;掺杂后,在费米能级处可以提供更多的填充电子,使得电子跃迁至导带更容易,固溶体的导电性增强。为Sn_1-xRu_xO₂固溶体电极材料的发展和应用提供了理论基础。     

Thermal Decomposition of Ti<Subscript>5</Subscript>(Se,Te)<Subscript>8</Subscript> in Argon and Nitrogen Atmospheres

Chalcogenides TiSe_1.60−x Te_x (0 ≤ x ≤ 1.60), forming a continuous series of hexagonal solid solutions, were prepared by the direct ampule procedure. The thermal decomposition of TiSe_1.60−x Te_x was studied for the samples with x = 0, 0.16, 0.80, 1.44, and 1.60 in Ar and N₂ atmospheres in the course of heating from 25 to 1000°C. The selenide undergoes no weight loss under Ar, in contrast to the telluride which disproportionates and loses weight owing to the formation of volatile TiTe₂. At high temperatures, tellurides are more sensitive than selenides to the presence of nitrogen: The disproportionation is accompanied by the reaction of TiTe₂ with N₂, yielding low-volatile titanium nitride and free tellurium. Titanium selenide and telluride as components of the solid solutions behave similarly to the corresponding individual chalcogenides.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1063–1067.Original Russian Text Copyright © 2005 by Pankratova, Zvinchuk, Suvorov, Hatanpaa, Kozlov, Leskela.     

Cubic-BN nanocrystals synthesis by pulsed laser induced liquid–solid interfacial reaction

Cubic boron nitride (c-BN) nanocrystals have been synthesized by pulsed laser induced liquid–solid interfacial reaction. It is shown that the diameters of the prepared quasi-spherical c-BN nanocrystals vary from 30 to 80 nm via transmission electron microscopy (TEM). The 2θ values of the X-ray diffraction (XRD) peaks of the resultant c-BN nanocrystals are 43.16°, 74.16°, 90.08° and 136.1°, respectively, corresponding to the (1 1 1), (2 2 0), (3 1 1) and (3 3 1) crystalline planes of a c-BN phase. Fourier transform infrared (FTIR) spectroscopy has also been used to characterize the structure of boron nitride. The formation of c-BN nanocrystals upon pulsed laser ablation at the liquid–solid interface is discussed in detail.     

Adsorption, electrophysical, and optical studies of the surface of solid solutions and the binary components of the InSb-ZnTe system

Piezoquartz microweighing, surface electroconductivity measurements, and IR and Raman spectroscopies were used to study the mechanism and regularities of the interaction of carbon monoxide, ammonia, and oxygen, gases of different electronic natures encountered in the environment and various technological processes, with the surface of solid solutions and the binary compounds of the InSb-ZnTe system. An analysis of the results with the use of the acid-base and other physicochemical characteristics of the adsorbents and of the electronic properties of the adsorbate molecules showed that the values of adsorption of the gases lie within α = 10⁻⁵−10⁻³ mol/m². It was demonstrated that, at temperatures above 293 K, the adsorption of CO and NH₃ occurs by the donor-acceptor mechanism, whereas oxygen is adsorbed through the ion-radical mechanism, with the predominant participation of coordinatively unsaturated metal atoms and vacancy defects, respectively. It was revealed that the acid-base, adsorption, electrophysical, and optical properties vary similarly with changing composition of the system, a behavior that suggests the same origin of adsorption sites and inherent surface states and makes it possible to predict the adsorption activity of a surface on the basis of its acid-base properties and the properties of the binary compounds and constituent elements. Similarities and distinctions in the behavior of (InSb) _x (ZnTe)_{1 − x} solid solutions and the binary compounds (InSb and ZnTe) were identified. Specific features of solid solutions, as multicomponent systems, are that adsorption on them is energetically more favorable, especially well pronounced in the acid-base characteristic-composition and adsorption characteristic-composition diagrams. Such diagrams made it possible to determine the solid solution most active with respect to ammonia, (InSb)_0.95(ZnTe)_0.05, which was used to make a selective high-sensitivity gas sensor.     

Effect of Anion Position on the Electronic Energy Structure of CuGaS2 and AgGaS2

The effect of the anion displacement parameter (u) on the local partial and total densities of electronic states is investigated for two chalcogenides of A^IB^IIIC ₂ ^VI type: CuGaS₂ and AgGaS₂. The forbidden gap (E_g) of the compounds is estimated. The calculations were performed in the framework of the cluster version of the local coherent potential approximation. It is established that E_g is a linear function of u. The curves of the local partial densities of states permit the estimation of the dependence of the splitting of the characteristic maxima on the chosen value of u; this dependence is also linear.     

Electron energy structure and X-ray spectra of wide-band GaN, AlN, and AlN-GaN semiconductors

The electronic energy structure of GaN, AlN, and AlGaN crystals with the wurzite structure is calculated by the local coherent potential method using the cluster version of the MT-approximation within the framework of the multiple scattering theory. The calculated densities of electron states are compared with XPS spectra of gallium and aluminum, AlL _{II, III} XES, and also with K-spectra of gallium and AlL _{II, III} XAFS absorption. The comparison of the electronic structure of Al_xGa_1?x N crystals and binary GaN and AlN and the interpretation of their features are performed. The concentration dependence of the width of the upper subband of the valence band and the band gap in Al_xGa_1?x N (x = 0, 0.25, 0.5, 0.75, 1) crystals on the content of aluminum is studied and its non-linear character shown.     

Influence of partial substitution of zinc for copper on electronic structures of YBa2Cu3O y

Summary By use of an approximate band-structure treatment based on the EHMO approach, the energy band structures for the Zn-doped superconductor YBa₂Cu_3–x Zn _x O _y were calculated in the present paper and the influence of partial substitution of zinc for copper on the electronic structures for orthorhombic YBa₂Cu₃O_y was studied. From analysis of the band structures and the densities of states for YBa₂Cu_3–x Zn _x O _y , it was demonstrated that the 2D Cu-O planes in the Y-Ba-Cu-O superconducting system have a direct and dominant influence on superconductivity, whereas the role of the 1D Cu-O ribbons and the O(4) atoms is also of some importance.