The defect structure of CdTe: Hall data

A high-temperature Hall effect study as function of cadmium pressure and temperature was carried out for pure and indium-doped CdTe. The results, combined with published data on the Hall effect of quenched crystals and electronic energy level positions, are interpreted on the basis of a detailed point defect model. Parameters of the equilibrium constants of various defect formation reactions are given.     

The logical structure of physicochemical data: Problems of numerical data standardization and exchange

The creation of voluminous databases on the physicochemical properties of substances requires a solution to the general problem of the variability of the logical structure of data. Logical structure variations, which manifest themselves by the differences in the volume, type, and content of data, the appearance of new characteristics, and changes in the rules for the identification of substances, can be caused by many reasons related to both the diversity of types of compounds and the necessity of the integration of data from various sources. The concept of semistructured data is considered; such data are optimum for the transfer of information about the properties of substances. The general principles for constructing the structure of data are formulated. These principles allow tuning to an arbitrary region of objects with the special features of objects (substances or atom-molecular structures) characteristic of it. The suggested concept is compared with the language developed recently within the framework of the IUPAC project for the standardization of exchange and dissemination of thermodynamic data.     

Self-diffusion of reversibly aggregating spheres

Reversible diffusion limited cluster aggregation of hard spheres with rigid bonds was simulated and the self-diffusion coefficient was determined for equilibrated systems. The effect of increasing attraction strength was determined for systems at different volume fractions and different interaction ranges. It was found that the slowing down of the diffusion coefficient due to crowding is decoupled from that due to cluster formation. The diffusion coefficient could be calculated from the cluster size distribution and became zero only at infinite attraction strength when permanent gels are formed. It is concluded that so-called attractive glasses are not formed at finite interaction strength.     

Self-diffusion in melts of statistical copolymers: The effect of changes in microstructural composition

We have used nuclear reaction analysis to measure diffusion coefficients D in couples consisting of hydrogenated polybutadienes of structure (C₂H₃(C₂H₅))_x(C₄H₈)_1?x and their partly deuterated counterparts. The 1,2- and 1,4-olefinic isomers are randomly distributed along the chains and the mean vinyl fraction x varies between 0.38 and 0.94. We find that the effective monomeric mobility D₀ [defined by D = D₀(N_e/N²) for each copolymer, where N is the backbone length and N_e the entanglement spacing] decreases monotonically with increasing vinyl content x. Over the range of microstructures and temperatures T (?14?40°C) investigated we find log(D₀/T) varies smoothly with (T ? T_g), where T_g is the glass transition temperature of the respective melts. An analysis of our data in terms of a simple activated rate process model suggests that D₀ is controlled by thermally activated hopping of segments whose effective volume is close to that of the respective statistical segment lengths of the copolymeric chains. ©1995 John Wiley & Sons, Inc.     

Self-assembly of CdTe nanoparticles into dendrite structure: a microsensor to Hg2+

A novel microsensor to Hg(2+) was fabricated through self-assembly of aqueous CdTe nanoparticles (NPs). The morphologies of self-assembly mainly included classical dendrites, straight dendrites, and small islands. The formation process of these morphologies was systematically investigated by using the field emission scanning electron microscope, confocal laser scanning microscope, and atom force microscope instruments, etc. The proposed mechanism showed that the dendrite structure was formed via manipulating the short-range van der Waals interaction and long-range electrostatic interaction, which was realized through altering the ligand and concentration of the CdTe NPs. Furthermore, polymers with positive charges were used to effectively control the morphology of the self-assembly as well as improve the property of photoluminescence. These CdTe dendrites were used as microsensors to Hg(2+), which presented the advantages of low cost, quick detection time, high selectivity, and easy operation.     

Unique structure and photoluminescence of Au/CdTe nanostructure materials

Unique nanostructure materials with highly ordered spherical aggregates have been obtained by self-organization of single CdTe nanocrystals using gold nanoparticles as seeds, and a red shift of the photoluminescence peak was observed.     

Self-diffusion coefficients and structure of the trivalent transplutonium ion curium and gadolinium in aqueous solution

Self-diffusion coefficients D of the trivalent aquo ion Cm³⁺ have been determined in aqueous Nd(ClO₄)₃?HClO₄ solutions (pH 2.5) at 25°C, by the open-end capillary method (O. E. C. M.). The variation of D versus the square root of the concentration of inactive solution is an exponential form in the studied range of concentration. The limiting value D₀ at zero ionic strength is 6.0·10^?6 cm²·s^?1. The curve \(D = f(\sqrt c )\) relating to Cm³⁺ can be compared to those of²⁴¹Am³⁺ and¹⁵³Gd³⁺ obtained under similar conditions. We find a similar ionic structure of Cm³⁺ with Am³⁺ and Gd³⁺. They have the same hydration as a tripositive of 5f and 4f ions in the absence of hydrolysis, complexing, or pairing at pH 2.5. The present study contributes to show the analogy of the solvation structure of trivalent actinide ions in aqueous solution at pH 2.5 with that of the trivalent lanthanide ions as a help for predicting the thermodynamic properties.     

The defect structure of anion excess CaF2

Neutron scattering and computer simulation techniques have been used to investigate the defect cluster structure of CaF₂ doped with 5% La^3?. The results strongly support the formation of small discrete clusters rather than the superstructures that have been suggested in recent studies of anion excess fluorites. The type of cluster that emerges as dominant comprises an interstitial-dopant dimer (of the 2:2:2 type) which has captured an additional F^? interstitial. The formation of such clusters is supported by recent ITC studies.     

Stable structure and effects of sulfur in CdTe/CdS heterojunctions

Structural and electronic properties of S in the CdTe/CdS(0001) interface are studied using the density functional theory. The interstitial S atom may induce the inversion of the surface Cd atoms and sublayer Te atoms of the Cd‐terminated surface, while S atoms may adsorb at the top sites, substitute Te atoms or accumulate at the voids inside the Te‐terminated (111) CdTe surface. Isovalent substituting S for Te in the CdTe(111)/CdS(0001) heterojunctions can reduce the strain arising from lattice mismatch and cause a reduction of interface states, so it may be better for solar cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Self-diffusion of a polystyrene-polyisoprene block copolymer

Forced Rayleigh scattering (FRS) has been used to measure the self-diffusion coefficient, D, of a lamellar-forming polystyrene-polyisoprene diblock copolymer (M_PS = 1.0 X 10⁴, M_PI = 1.3 X 10⁴) as a function of temperature. The measurements traverse the order-disorder transition (ODT), which occurs at 160°C. There is no obvious change in either D or the temperature dependence of D at the ODT, in agreement with measurements on several other systems. Electron microscopy confirms that the sample in the ordered state is quenched, with no long-range orientation of lamellae, and a typical grain size well below 1 μm. In contrast to previous measurements on a similar styrene-isoprene diblock, these FRS signals are well-described by single exponential decays; this may be largely attributed to differences in average grain size. The temperature dependence of D is modeled with several empirical expressions, based on the known monomeric friction factors for pure polystyrene and pure polyisoprene, but without quantitative success. These results underscore the need for a greater understanding of the composition and temperature dependences of local friction in polymer mixtures. © 1996 John Wiley & Sons, Inc.     

Thermodynamic data bank: The principles, organization, and structure of software

The structure and special features of a software for work with a data bank are described. A method for storing thermodynamic information about mineral and gas phases and solution components is suggested. The purpose of the creation of the data bank was the provision with the initial thermodynamic data and programs that minimized the Gibbs energy for the solution of physicochemical simulation problems and the construction of mineral equilibrium diagrams. The possibilities of the software were demonstrated for the example of the construction of mineral equilibrium diagrams for minerals containing rare-earth metals.     

The use of calorimetric data for estimation of the point defect concentration in solids

Calorimetric methods which allow estimation of the point defect concentration in solids are reviewed. Special attention is paid to the calculation of defect parameters based on the analysis of excessive heat capacity, and to correlations between the thermodynamic parameters of melting and the energetic parameters of point defect formation. The applicability of the thermodynamic approach to the study of intrinsic disorder in solids is demonstrated.

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Zusammenfassung Kalorimetrische Methoden zur Abschätzung der Konzentration von Punktdefekten in Festkörpern werden zusammengestellt. Aufmerksamkeit verdienen die Berechnung von Defektparametern aus einer Untersuchung der Exzeß-Wärmekapazität und Korrelationen zwischen thermodynamischen Parametern des Schmelzens und energetischen Parametern der Punktdefektbildung. Die Anwendbarkeit eines thermodynamischen Ansatzes zur Untersuchung der Eigenfehlordnung in Festkörpern wird demonstriert.

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The structure of defect Ru4Si3

The nature of the defect structure of Ru₄Si₃ has been studied with electron diffraction and electron microscopy methods. Lattice image pictures, interpreted with histogram analysis, reveal that planar defects of chemical twinning type are common in the crystals.     

The defect structure of V4As3

The nature of the defect structure of crystals of V₄As₃ has been studied by electron diffraction and electron microscopy methods. Lattice images reveal that planar defects of the chemical twinning type are common in the orthorhombic α-V₄As₃ crystals. Thermal decomposition, yielding negative crystals, was also studied.     

液体分子自扩散系数的预测

基于液体层膜结构模型提出预测液体分子自扩散系数的方程,对24种液体在较宽温度范围内作了检验,平均偏差为3.8%。同时分析了层膜结构模型中位形参数ξ随温度和物质不同而变化的规律,这对了解液体的微观结构、扩散过程的机理和阐明层膜结构模型的合理性具有重要意义。     

On the defect structure in nonstoichiometric metal oxides

A number of important physical and chemical properties of nonstoichiometric transition metal oxides are influenced by kind and concentration of defects in the crystalline lattice of these materials. Until quite recently it was thought that the relation between the nature of defects in the lattice of these oxides and their physical and chemical properties could be explained satisfactorily based on point defect theory. Today it is known that such an approach is correct only in the case of very small defect concentrations. At higher concentrations the mutual interaction between point defects results in formation of complexes and defect clusters called extended defects. These extended defects can become further ordered, which leads to superstructure ordering and to formation of intermediate phases. In some cases point defects can become eliminated in the process of crystallographic shear which is connected with formation of a whole series of intermediate phases.     

Anion and cation defect structure in magnesium fluorogermanate

Single crystals of magnesium fluorogermanate have been grown from a melt composition of 3.5MgO·0.5MgF₂·GeO₂ in a lead fluoride flux. The crystals are isomorphous with magnesium germanate, Mg₂₈Ge₁₀O₄₈; the space group is Pbam and a = 14.343(1), b = 10.196(1), and c = 5.9075(4) Å. A final unit cell composition of Mg₂₈Ge_7.5O₃₈F₁₀ was deduced from a detailed analysis of high quality X-ray diffraction data. A residual, R = 0.045, was achieved with a data-parameter ratio of 17 in the final anisotropic refinement.