Diffusion process of sodium ions in the transition of the bronze-type sodium titanium dioxide

Sodium-ordered Na_xTiO₂ is transformed into its disordered form by way of a new ordered form. All forms have the same crystal structure framework and monoclinic symmetry. When a, b, and c represent the lattice vectors of C-centered unit cells in the disordered form, the starting ordered form has a C-centered lattice of 2a, 4b, and c, and the new ordered form has a primitive lattice of a, b, and c. Sodium ions make one-dimensional diffusion along the b axis in the first phase change and two-dimensional diffusion parallel to the ab plane in the subsequent transformation. Two stages of diffusion correspond to two kinds of interstitial paths in the framework. Crystallites of the starting ordered arrangement are often divided into many domains with respect to the sodium arrangement. The present diffusion mechanism suggests that the initial arrangement changes directly into the final disordered one in the vicinity of domain boundaries.     

Order and disorder in Ca2ND0.90H0.10-A structural and thermal study

The structure of calcium nitride hydride and its deuterided form has been re-examined at room temperature and studied at high temperature using neutron powder diffraction and thermal analysis. When synthesised at 600 °C, a mixture of both ordered and disordered Ca₂ND_0.90H_0.10 phases results. The disordered phase is the minor component and has a primitive rocksalt structure (spacegroup Fm3m) with no ordering of D/N on the anion sites and the ordered phase is best described using the rhombohedral spacegroup R-3m with D and N arranged in alternate layers in (111) planes. This mixture of ordered and disordered phases exists up to 580 °C, at which the loss of deuterium yields Ca₂ND_0.85 with the disappearance of the disordered phase. In the new ordered phase there exists a similar content of vacancies on both anion sites; to achieve this balance, a little N transfers onto the D site, whereas there is no indication of D transferring onto the N-sites. These observations are thought to indicate that the D/N ordering is difficult to achieve with fully occupied anion sites. It has previously been reported that Ca₂ND has an ordered cubic cell with alternating D and N sites in the [100] directions [1]; however, for the samples studied herein, there were clearly two coexisting phases with apparent broadening/splitting of the primitive peaks but not for the ordered peaks. The rhombohedral phase was in fact metrically cubic; however, all the observed peaks were consistent with the rhombohedral unit cell with no peaks requiring the larger ordered cubic unit cell to be utilised. Furthermore this rhombohedral cell displays the same form of N-D ordering as the Sr and Ba analogues, which are metrically rhombohedral.     

The crystal structure of copper bromide telluride

The crystal structure of CuBrTe has been determined. The compound is tetragonal with unit cell dimensions a = 16.417Å, c = 4.711Å, Z = 16, and space group I4₁/amd. Three-dimensional counterdiffraction intensity data (MoKα) were refined with full-matrix least-squares to a conventional unweighted R of 0.066. The structure consists of infinite tellurium spirals with bromine tetrahedra interspersed. Two basic types of disordered copper atoms were found. One type is at the center of the bromine tetrahedra and has several possible locations for each atom. The other type of copper lies on two possible sites in a distorted tetrahedral environment with tellurium and two bromine atoms as nearest neighbors.     

Structural and Magnetic Chemistry of La2Sr2BMnO8 (B=Mg, Zn)

Polycrystalline samples of the layered perovskites La₂Sr₂MgMnO₈ and La₂Sr₂ZnMnO₈ have been studied by X-ray and neutron powder diffraction, electron diffraction and magnetometry. X-ray and neutron powder diffraction indicate that the average structure is that of K₂NiF₄, with disordering of Mn and (Zn, Mg) cations over the octahedral sites. Electron diffraction data indicate that cation ordering is present over these sites in the xy planes, with the xy ordered planes being stacked in a disordered manner along z. No long-range magnetic ordering is observed in the temperature range 5≤T (K)≤300.     

Photometric determination of copper(II) in nickel alloys using azoderivatives of ethyl acetoacetate

1-Ethoxy-2-(2-hydroxy-3-sulfo-5-chlorophenylazo)butane-1,3-dion (L₁), 1-ethoxy-2-(2-hydroxy-3,5-disulfophenylazo)butane-1,3-dion (L₂), 1-ethoxy-2-(2-hydroxy-4-nitrophenylazo)butane-1,3-dion (L₃), and 1-ethoxy-2-(2-hydroxyphenylazo)butane-1,3-dion (L₄) were synthesized on the basis of ethyl acetoacetate, and their analytical characteristics were studied. The following dissociation constants of the reagents were determined by potentiometric titration: pK ₁ = 5.94 ± 0.04 and pK ₂ = 9.75 ± 0.04 (L₁), pK ₁ = 5.78 ± 0.02 and pK ₂ = 9.55 ± 0.03 (L₂), pK ₁ = 6.03 ± 0.03 and pK ₂ = 9.86 ± 0.05 (L₃), and pK ₁ = 6.19 ± 0.05 and pK ₂ = 9.98 ± 0.06 (L₄). The chemical analytical characteristics of copper(II) complexes of L₁–L₄ were determined by spectrophotometry. It was found that, with an increase in the elecrophilic properties of the substituents introduced into the aromatic ring of the molecule, the sensitivity of the reaction increased; the substituents had no effect on the ratio of Cu : L = 1 : 2. A photometric procedure was developed for determining copper in nickel-based alloys.     

How does the accuracy of NMR conformational analysis depend on the equilibrium constant?

Analytical expressions are derived for the analysis of the accuracy of NMR determinations of conformational equilibrium constants, K. The relative error, σ_K/K, shows a nearly linear increase with K for two commonly used modifications of the NMR approach to conformational analysis (based on measurements of integral intensities and averaged chemical shifts).     

Determination of bismuth, selenium and tellurium in nickel-based alloys and pure copper by flow-injection hydride generation atomic absorption spectrometry—with ascorbic acid prereduction and cupferron chelation-extraction

Diverse matrix effects on the determination of bismuth, selenium and tellurium (μg g⁻¹) in nickel-based alloys and pure copper by flow-injection hydride generation atomic absorption spectrometry (FIAS-HGAAS) were investigated. Sodium tetrahydroborate was used as the reductant. The separation of analytes from copper matrix was mandatory while the analytes were successfully determined without being separated from the alloy matrix. Hydrochloric acid was effective in the prereduction of bismuth and selenium, however, it did not give any satisfactory result for tellurium in nickel-based alloys. In this work, 5% (w/v) ascorbic acid was proved effective for the prereduction of tellurium.Successful determination of tellurium in copper was achieved when N-nitroso-N-phenylhydroxylamine (cupferron) chelation-extraction was employed for the separation of tellurium from copper matrix. Cupferron chelation-extraction was performed in phosphate buffer (a mixture of 0.2 mol l⁻¹ sodium phosphate and 0.1 mol l⁻¹ citric acid). Lanthanum hydroxide coprecipitation at pH 10.0±0.5 was effective for bismuth and selenium. Standard reference materials of nickel-based alloys and pure copper were analyzed using the proposed methods. The linear range for the calibration curves were 0.30-15 and 0.20-10 ng ml⁻¹ for BiH₃ and H₂Se, respectively, with a correlation coefficient of 0.9995. For H₂Te, the linear range for the calibration curves was 0.50-12 ng ml⁻¹ with the correlation coefficient of 0.9994. Good agreement was obtained between experimental values and certified values. Satisfactory recovery ranged from 91±1 to 106±2% was obtained from five replicate determinations.     

High-sensitivity methods for sequential injection determination of the main constituents of alloys

A sequential injection system with spectrophotometric detection was proposed for the determination of copper, zinc and lead in brass. In view of the high analyte concentrations and the sensitivity of the involved catalytic methods, optimization of the flow system was carried out aiming mild reaction conditions. Copper and lead determinations were based on the catalytic effects of Cu²⁺ and Pb²⁺ on the oxidation rates of resorcinol and pyrogallol red by H₂O₂, respectively, and zinc determination involved precipitate formation after oxidation of 1-nafthylethylenediamine by K₃Fe(CN)₆. The analytical procedures were designed with some common parameters such as pH=9.0 (borate system), λ=530 nm, and H₂O₂ as oxidizing agent; system geometry was maintained.The proposed system is rugged, and base line drift is not observed during 4 h operation periods. Twenty samples are run per hour (60 determinations) and reagent consumption is minimal, thus avoiding drawbacks related to waste management. Precise results (R.S.D.<1.0%; n=7) are obtained and a detection limit of 1% (w/w) was estimated for the three analytes. Results were in agreement with flame atomic absorption spectrometry.     

Cu22Bi12S21Cl16—A mixed conductor with fast one-dimensional copper(I) ion transport

Melting reactions of Cu, CuCl, S, and Bi₂S₃ yield black, shiny needles of Cu₂₂₍₁₎Bi₁₂S₂₁₍₁₎Cl₁₆₍₁₎. The compound decomposes peritectically at 649(5) K. Oxidation state +I of the copper atoms is supported by Cu-K-XANES. The compound crystallizes in the hexagonal space group P6/m with a=2116.7(7) pm and c=395.17(5) pm. Seven anions coordinate each of the two independent bismuth cations in the shape of mono-capped trigonal prisms. These polyhedra share edges and faces to form trigonal and hexagonal tubes running along [0 0 1]. The hexagonal tubes are centered by chloride ions, which are surrounded by disordered copper cations. The majority of copper cations are distributed over numerous sites between the tubes. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [0 0 1]. The high mobility of the copper cations along [0 0 1] was demonstrated by impedance spectroscopy and DC polarization measurements on single crystals. The ionic conductivity at 450 K is about σ_ion=0.06 S cm⁻¹, and the activation energy for Cu⁺ ion conduction is E_a=0.44 eV. The chemical diffusion coefficient of copper is in the order of D_cu^δ=10¹⁹ cm⁻³ at 420 K. The electronic band gap (p-type conductor) was determined as E_g=0.06 eV. At room temperature the thermal conductivity of a pressed pellet is about κ=0.3 W K⁻¹ m⁻¹ and the Seebeck coefficient is S=43 μV K⁻¹.     

Calculation of the stability of nonperiodic solids using classical force fields and the method of increments: N2o as an example

Combining classical force fields for the Hartree–Fock (HF) part and the method of increments for post‐HF contributions, we calculate the cohesive energy of the ordered and randomly disordered nitrous oxide (N₂O) solid. At 0 K, ordered N₂O is most favorable with a cohesive energy of ?27.7 kJ/mol. At temperatures above 60 K, more disordered structures become compatible and a phase transition to completely disordered N₂O is predicted. Comparison with experiment in literature suggests that experimentally prepared N₂O crystals are mainly disordered due to a prohibitively high activation energy of ordering processes. © 2015 Wiley Periodicals, Inc.     

Anwendbarkeit der flammenlosen Atomabsorption in der messenden komplexchemie: Verteilung von Cu(II) zwischen chloroform und wasser in Gegenwart von 8-hydroxychinolin

Atomic-absorption spectrophotometry with the graphite furnace atomizer has been used in a study of the extraction equilibria of copper oxinate. The amounts of copper back-extracted from chloroform solutions of oxine into aqueous solutions containing tetramethyl ammonium nitrate were determined, and the stability constants β₁ and β₂, and the distribution coefficient K_N for copper oxinate, were then calculated. The protonation constants K₁ and K₂ for the oxinate anion and the distribution coefficient K_HL for oxine were determined by potentiometric aqueous and two-phase titrations respectively. The values obtained are in good agreement with published data.     

Anomalous density effect near the interface between two media

A theoretical investigation is presented for the local energy loss of a relativistic charged particle and theK-shell excitation cross section σ _K when the particle crosses a sharp interface between two different media. The logarithmic increase of the local energy loss andσ _K with the particle energy is shown to differ essentially from the case of a homogeneous medium. The calculations ofσ _K for aluminum and copper foils are in good agreement with the experimental data.     

Dissociation constants of Br∅nsted acids in D2O and H2O: studies on polyaza and polyoxa-polyaza macrocycles and a general correlation

Using data on a series of polyaza and polyoxa-polyaza macrocyclic compounds, a satisfactory linear correlation was established between the dissociation constants of their acid forms obtained in deuterium oxide (pK_D) and in water (pK_H). The isotopic effect, ΔpK=pK_D - pK_H, increases with increasing pK, being larger for the weaker acids. The pK_D vs. pK_H correlation may be used to determine pK_D or pK_H values when one of the constants is known; the statistical errors of the estimates are not significatively higher than those of the experimental determinations. By including data available in the literature for a series of different acids (mineral and carboxylic acids, phenols, protonated amines, amino acids, etc.; a total of 138 pairs of data for 70 different compounds), a good general pK_D vs. pK_H correlation was also obtained (correlation coefficient 0.998), showing that the dependence of the isotopic effect on the nature of the acid is not as important as previous studies, based on limited and not always satisfactory Δpk vs. pK_H correlations, suggested.     

The Precision of KM Determinations: A Rapid Evaluation

Abstract

An algebraic method is presented for the evaluation of the precision of K_m determinations in terms of the accuracy of the assay procedure     

The crystal structure of the 42-Å subcell of a layer structure with approximate composition Ba4Nb2S9

Platy crystals from the products of a mixture 4 Bas : 2 Nb : 5 S reacted at 1000°C have cell constants a = 13.754(3) Å, c = 83.73(2) Å, $\text{R}\text{3}\text{m}$. The reciprocal lattice had a pronounced subcell with dimensions a = 6.877(1) Å, c = 41.84(1) Å, same space group. Three dimensional X-ray diffraction data were collected using monochromatized Mo Kα radiation and of 5051 measured intensities 1892 were considered observed. From the set of observed intensities 611 reflections having all even indices were used to refine the crystal structure of the 42 × 7-Å subcell. The final R = 0.036 and ωR = 0.052 for the 611 observed amplitudes and R = 0.046, ωR = 0.052 for all 711 amplitudes of the subcell. The structure is based on the stacking of hexagonal BaS₃ layers with the sequence DABABDBCBCDCACAD. The D layer denotes a disordered level and occurs at $\text{z = 0,}\text{1}\text{3}$ and $\text{2}\text{3}$. The different letters for the ordered layers are based on the Ba positions in that layer. The Nb ions occupy octahedral interstices and form a unit of three face sharing octahedra parallel to c. The column is terminated above and below by disordered levels. The NbNb distances are 3.22 Å, causing displacement of Nb from the centers of the two outside octahedra. One Ba is in the center of a triangular orthobicupola formed by 12 S atoms. The other Ba is in the center of a hexagon of 6 S with 3 additional S above this layer forming $\text{1}\text{2}$ of a cuboctahedron. The lower half consists of a disordered layer of atoms. The NbS distances are 2.279, 2.433, and 2.683 Å; BaS distances vary between 3.1 and 3.5 Å. The subcell content based on the ordered structure only is Ba₁₂Nb₉S₃₆. The placement of disordered Ba and S at $\text{z = 0,}\text{1}\text{3}$, and $\text{2}\text{3}$ levels of the subcell leads to the unlikely composition Ba_16.5Nb₉S₄₂. The ordered structure most likely has a composition Ba₄Nb₂S₉, z = 36, so that the subcell composition should be Ba₁₈Nb₉S_40.5. The completely ordered structure has not been solved.     

Effect of heat treatment on the structure of L-Ta2O5:: a study by XRPD and HRTEM methods

The effect of heat treatment on the structure of L-Ta₂O₅ has been studied by X-ray powder diffraction and high-resolution transmission electron microscopy, complemented by density measurements. Two stable low-temperature forms of L-Ta₂O₅ were found: one below about 1000°C with a b^* multiplicity of m≈13.5 and the other at 1350°C with m=11. The former modification was disordered, containing defects and twins, while the latter seemed to be more ordered. At intermediate temperatures, ordered and disordered mixtures of L-Ta₂O₅ slabs with m values in the range m=11-14 were seen. A new model of a structure of L-Ta₂O₅ (m=11) is proposed. The model can be described as an ordered intergrowth of slabs of α-U₃O₈ and β-U₃O₈ types. The α-U₃O₈ slabs are wider and contain somewhat larger three-sided tunnels that appear to be more suitable for interstitial Ta atoms than the β-U₃O₈ slabs. The density measurements confirm that additional Ta atoms are present in the structure.     

Synthesis and crystal structure of (2.2.2-cryptand)potassium perchlorate

A new complex (2.2.2-cryptand)potassium perchlorate [K(Crypt-222)]ClO₄ is synthesized, and its structure is studied by X-ray diffraction analysis (space group R32, a = 8.441 Å, c = 30.475 Å, Z = 3). The structure is solved by the direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.032 for 1222 independent (with allowance for anomalous dispersion) reflections (CAD4 automated diffractometer, λMoK _α radiation). The centers of the ClO ₄ ^? anion and [K(Crypt-222)]⁺ complex cation are in the positions (0,0,0) and (0,0,1/2), respectively, with the point symmetry 32. The ClO ₄ ^? anion is randomly disordered. The complex cation (with the high symmetry D ₃) is of the host-guest type and is somewhat disordered and exists as two different conformations with probabilities of 87 and 13%. The coordination polyhedron of the K⁺ cation (coordination number 8) is a two-base-centered trigonal prism distorted toward antiprism.     

Influence of the alloying effect on nickel K-shell fluorescence yield in Ni–Si alloys

Alloying effects on the K-shell fluorescence yield ω_K of nickel in Ni–Si binary alloy system have been studied by energy dispersive X-ray fluorescence. It is found that ω_K increases from pure Ni to Ni₂Si and then decreases from Ni₂Si to NiSi. These results are discussed in terms of d-occupation number on the Ni site and it is concluded that electronic configuration as a result of p-d hybridization explain qualitatively the observed variation of ω_K in Ni–Si alloys.     

The determination of the ionisation constants of polymaleic acid and the stability constants of its complexes with copper

The ionisation constants of unfractionated polymaleic acid, H₃A, a synthetic analogue of fulvic acid, and the stability constants of its copper complexes were determined by differential pulse polarography. The ionisation constants are: pK₁ 5.16, pK₂ 7.04 and pK₃ 9.82 at 20° C and ionic strength 0.12 M. The stability constant of the CuHA complex, which is the predominant species at pH 5–9, lies in the range log (CuHA) = 7.15–8.7; the mean value is 8.17.     

Intermetallic compounds and the determination of copper and zinc by anodic stripping voltammetry

The intermetallic CuZn compounds produced during the simultaneous deposition of copper and zinc at a preformed mercury film electrode were studied. Over a wide range of metal concentration ratios, the real concentrations of metals in the amalgam were calculated from the peak areas obtained by anodic stripping voltammetry. The results indicate the formation of CuZn (insoluble) and CuZn2 (soluble) compounds with K_so=5×10^?4 and β₂=100, respectively. The electrodeposition potential of ?0.85 V vs. SCE for the reduction of copper in presence of zinc is confirmed as correct.