Electrochemical intercalation of hydrated cations derived from primary amines into 2H-NbS<Subscript>2</Subscript>

We report the electrochemical intercalation of three cations derived from amines with different chain length, into the layered compound 2H-NbS₂. The intercalation processes were accompanied by ex situ and in situ X-ray diffraction. For in situ analysis, an electrochemical cell was designed for the purpose. The X-ray diffraction experiments show that the intercalation is a complex process, which involves stacking faults and the formation of stages. When the cations are removed, no changes in the final interplanar basal distances occur, suggesting that there are ideal concentrations of intercalated ions that stabilize the phases. Also, based on the X-ray diffraction results we propose a steric arrangement for the hydrated cations into the van der Waals gaps.     

Grain size effect on diffusion processes in superionic phases Cu<Subscript>1.75</Subscript>Se,Li<Subscript>0.25</Subscript> Cu<Subscript>1.75</Subscript>Se,and Li<Subscript>0.25</Subscript> Cu<Subscript>1.75</Subscript>S

Ionic conduction and chemical diffusion in Cu_1.75Se, Li_0.25 Cu_1.75Se, and Li_0.25Cu_1.75S at 140–240°C are studied. The ionic conduction of Cu_1.75 Se is shown to increase with the average grain size. With coarsening of grains, the activation energy for ionic conduction decreases in Cu_1.75Se and increases in Li_0.25Cu_1.75S. The reasons for the diffusion effects observed in the studied materials are discussed.     

Physicochemical Properties of Li<Subscript>6</Subscript>V<Subscript>5</Subscript>O<Subscript>15</Subscript> as the Cathode Material for Lithium-Ion Batteries

Lithium-vanadium oxide with the formal composition Li₆V₅O₁₅, uniform microsctructure, and the particle size of 100 nm is synthesized by a solution method. The synthesized compound is characterized by the methods of X-ray diffraction analysis, Raman spectroscopy, and synchronous thermal analysis. The total electric conductivity is measured by the method of impedance spectroscopy and its electronic component is estimated by dc method. In the temperature range of 200–400°C, Li₆V₅O₁₅ represents a mixed electronic- ionic conductor with predomination of the ionic component and is thermally stable up to 550°С. Preliminary tests of a laboratory model of electrochemical cell Li|LiPF₆|Li₆V₅O₁₅ are carried out.     

Chemical bonding and electronic structure of LaMnO<Subscript>3</Subscript> and La<Subscript>0.75</Subscript>MnO<Subscript>3</Subscript> orthorhombic crystals

The electronic structure of the LaMnO₃ orthorhombic crystal of a stoichiometric composition and of La_0.75MnO₃ crystals with a La vacancy in the unit cell is calculated in the LSDA+U approximation of density functional theory. The calculations showed that LaMnO₃ is an insulator with a forbidden gap of 0.5 eV and with antiferromagnetic ordering of magnetic moments. The magnetic moment on the manganese ions is 3.78 BM. The La atom has ionic bonds in the lattice, while the bond between oxygen and manganese is covalent. After lanthanum has been removed, geometry optimization of the unit cell leads to La_0.75MnO₃ stable structures. In one of the structures, which is lower in energy, the states of manganese may be attributed to Mn⁴⁺ ions. In both structures with removed lanthanum, the oxygen ions have reduced effective charge, so that one can speak about O^? ions appearing along with O^2? in the structure. The oxygen, as well as lanthanum and manganese, ions are nonequivalent in these structures; their nonequivalence is primarily reflected by the local densities of states. This leads to charge and magnetic nonequivalence of ions. In La_0.75MnO₃ crystals, the degree of bond covalence between manganese and oxygen decreases.     

Quantum chemical modeling of possible reactions of mononuclear iron nitrosyl complex [Fe(SC(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>)<Subscript>2</Subscript>(NO)<Subscript>2</Subscript>]Cl•H<Subscript>2</Subscript>O in an aqueous solution

Possible reactions of the mononuclear iron nitrosyl complex [Fe(SC(NH₂)₂)₂(NO)₂]Сl?H₂O in an aqueous solution were studied using quantum chemical modeling. The electronic structures of the possible intermediates were examined by the NBO and AIM methods. The substitution of the thio ligand in the iron—sulfur nitrosyl complex by a water molecule and the formation of dimeric intermediate complexes were found to facilitate the NO-donation process.     

Phase Equilibria in the K,Cа∥SO<Subscript>4</Subscript>,CO<Subscript>3</Subscript>,HCO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O System at 25°С

Phase equilibria in the system K,Cа∥SO₄,CO₃,HCO₃–H₂O have been studied at 25°С. This system at 25°С involves 7 invariant points, 21 monovariant curves, and 22 divariant fields. The data gained served to plot the first phase diagram (phase complex) of the studied system at 25°С.     

Electronic-Ionic Processes in Bi<Subscript>2</Subscript>Cu<Subscript>0.5</Subscript>Mg<Subscript>0.5</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> with Pyrochlore Structure

Solid solution Bi₂Cu_0.5Mg_0.5Nb₂O_9–δ with the pyrochlore structure is synthesized by three different methods. Its structure and chemical composition are confirmed by X-ray diffraction analysis, electron microscopy, and energy-dispersive spectroscopy. The electronic-ionic processes are studied by the method of impedance spectroscopy in the frequency range from 0.3 Hz to 1.0 MHz and the temperature range from 0 to 340°С. The data are processed with the use of ZView program. Electrochemical models of samples are obtained in the form of equivalent circuits. The sign of the main charge carrier is determined by the thermo-emf method. Nonlinear effects are studied based on voltammetric characteristics. It is found that at room temperature, the charge in samples is transferred by electrons and cations (presumably, copper). In the temperature range of 260–300°С, the capacitance of samples and the specific conductivity of their volume demonstrate local minimums. Insofar as at these temperatures the oxygen conduction may occur, it is assumed that associates of anions and cations are formed. The decrease in the concentration of charge carries is confirmed by sample’s equivalent circuit into which the Gerischer impedance is introduced to enhance the accuracy. It is shown that at t = 260°С, the lifetime of charge carriers is the minimum.     

Resonant photoemission and absorption spectroscopy study of the Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiSe<Subscript>2</Subscript> electronic structure

The Cu3p and Cu2p resonance photoelectron spectra of the valence bands and core levels as well as Ti and CuL _2,3 absorption spectra for monocrystals 1T-Cu _x TiSe₂ were studied. The valence spectra obtained at Cu3p and Cu2p resonance drastically differ from each other. For Cu 3p-3d resonance, there are several bands corresponding to different channels of excited state decay. Spectra of the valence bands at Cu 2p-3d resonance are virtually identical to the spectra of pure TiSe₂. As follows from the absorption spectra, titanium atoms have the oxidation state 4+, whereas copper atoms are close to the free ion state.     

Thermodynamic study of Ag<Subscript>8</Subscript>GeSe<Subscript>6</Subscript> by EMF with an Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> solid electrolyte

The Ag–Ge–Se system was studied in the range of compositions Ag₂Se–GeSe₂–Se by measuring the EMF of the concentration (relative to the silver electrode) circuits with a solid electrolyte Ag₄RbI₅ in the temperature range 290–430 K. The polymorphic transition temperature of Ag₈GeSe₆ (320 K) was determined and the partial molar functions of silver were calculated for both crystal modifications of this compound based on the EMF measurements. The thermodynamic functions of formation and entropy of both modifications of Ag₈GeSe₆ and the thermodynamic functions of its polymorphic transition were calculated.     

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.     

Crystal structure and triboluminescence of centrosymmetric complex [Eu(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>(HMPA)<Subscript>3</Subscript>]

By single crystal X-ray analysis, the atomic structure of the crystals of [Eu(NO₃)₃(HMPA)₃] complex (HMPA is hexamethylphosphorotriamide) possessing intense triboluminescence is determined. Symmetry of centrosymmetrical crystals is monoclinic: a = 13.785(1) Å, b = 19.746(2) Å, c = 14.723(1) Å, β= 102.143(2)°, P2₁/n space group, Z = 4, d _x = 1.484 g/cm³. The crystal structure is represented by separate C₁₈H₅₄EuN₁₂O₁₂P₃ complexes linked by van der Waals interactions with pronounced cleavage planes. The coordination polyhedron of Eu(III) atom reflects the state of distorted square antiprism. The possible causes of spectral differences in the Stark structure of photo- and triboluminescence are discussed.     

Models of molecular structures of aluminum–iron clusters AlFe<Subscript>3</Subscript>, Al<Subscript>2</Subscript>Fe<Subscript>3</Subscript>, and Al<Subscript>2</Subscript>Fe<Subscript>4</Subscript> according to quantum-chemical DFT calculations

The geometrical parameters of molecular structures of three types of aluminum–iron clusters containing in total four, five, and six Al and Fe atoms in structural units have been calculated by the OPBE/TZVP density functional theory (DFT) method with the Gaussian09 program package. It has been found that the AlFe₃, Al₂Fe₃, and Al₂Fe₄ clusters can have four, eight, and nine structural modifications, which significantly differ in stability and geometric parameters. Bond lengths and bond and torsion (dihedral) angles are reported for each of these modifications.     

EPR of copper ions in Pb<Subscript>2</Subscript>MoO<Subscript>5</Subscript> crystals

The article presents the results of EPR studies of Pb₂MoO₅ crystals containing a copper impurity. Based on the analysis of angular dependences of the EPR spectra, it is found that copper ions incorporate into the structure of the Pb₂MoO₅ crystal in the Cu²⁺ state and occupy the molybdenum site with the formation of a linear extended Cu(II)–V(O)–Pb(IV) defect along the а axis of the crystal. An oxygen vacancy appears in the structure of the defect to compensate the charge and the lead ion acquires the Pb⁴⁺ charge state. According to the structure of this center, one magnetically non-equivalent position with the direction of main values of А and g of A(Cu)_zz and g_zz tensors parallel to the а axis is observed in the EPR spectra. Moreover, the EPR spectra exhibit an addition hyperfine structure from one lead atom on which the unpaired electron density is 0.061%. The obtained data on the structure of the defect formed when the copper impurity incorporates into the Pb₂MoO₅ crystal provided the assumption that the observed light scattering when the light beam is directed perpendicular to the а axis may be due to the cooperative effect of the presence of di- and tetravalent ions substituting for molybdenum in the linear configuration of Pb–O–Mo bonds.     

Charge Transfer and Defect Structure in BaCeO<Subscript>3</Subscript>

Electrical conductivity (at 460–990°С) and ion and proton transference numbers (at 550–950°С) of nominally undoped BaCeO₃ have been studied as dependent on temperature, pO₂ (2.1 × 10^–4 to 10–15 Pa), and pН₂O (40–2340 Pa). For determining the defect model, small additives of aliovalent dopants Nd³⁺ (up to 1 at %) and Ta⁵⁺ (up to 0.5 at %) were used. The effect of cationic nonstoichiometry of barium cerate on the electrical conductivity and reaction with the gas phase has been considered. Charge transfer in ВаСеО₃ is explained using the model of defect formation in the reaction of ВаСеО₃ with the gas phase.     

Neutron diffraction study of dehydrogenation of titanium carbohydrides TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The possibility of the synthesis of hydrogen-nonstoichiometric cubic titanium carbide ТiС _х of high purity from powdery nonstoichiometric cubic titanium carbohydride ТiС _х H _y or nonstoichiometric titanium carbide with admixture hydrogen by annealing in a continuously maintained vacuum of no worse than 1.33 × 10^–3 Pa at temperatures of 600–750°C for several hours has been shown. Similar annealing at higher temperatures (T ≥ 800°C) does not lead to the complete removal of hydrogen from a sample due to intensive sintering. In this case, it seems that pores between sintered particles are hydrogen traps, and the release of hydrogen through the surface of sintered particles is hindered.     

Cycling Performance at Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript>|Li Interface

Cyclability of the Li|Li₇La₃Zr₂O₁₂ interface was tested by voltammetry under externally applied potential difference. It was found that the solid electrolyte synthesized in the study contains a minor amount of an impurity in the form of lithium carbonate. This impurity forms, when brought in contact with metallic lithium, carbon that pierces the whole volume of the ceramic separator and produces a channel for a flow of electrons through the material, which leads to a poor cyclability of the solid electrolyte. A possible way to solve the given problem is via a purposeful replacement of the carbonate in the intergrain space of Li₇La₃Zr₂O₁₂ with another crystalline or glassy plasticizer that possesses an acceptable unipolar lithium conductivity (no less than 10^–6 S cm^–1) and forms, when brought in contact with metallic lithium, no electrically conducting compound or a compound capable of reversibly intercalating/deintercalating lithium.     

Crystal and molecular structures and luminescence properties of [Eu(Cin)<Subscript>3</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> complex

The crystal structure of europium cinnamate of the composition [Eu(Cin)₃] _n (Cin is cinnamic acid anion C₉H₇O ₂ ^? ) was determined by X-ray crystallography (a = 22.626(1) Å, c = 7.7330(7) Å, space group R3/c, Z = 3, ρ_calc = 1.448 g/cm³). The coordination polyhedron of Eu atoms is a distorted trigonal prism with three centered square faces. The structure is built of infinite polymeric chains [Eu(Cin)₃] _n running along the c axis and linked by van der Waals and π stacking interactions. Luminescent characteristics of the compound were determined.     

New mixed tellurides of nickel and Group 13–14 metals Ni<Subscript>3−δ</Subscript>MTe<Subscript>2</Subscript> (M = Sn,In, Ga)

Three new mixed tellurides of nickel and group 13–14 metals Ni_3−δMTe₂ (M = Sn, In, Ga) were prepared by high-temperature ampoule synthesis and studied by powder X-ray diffraction analysis. The compound Ni_3−δSnTe₂ was also studied by single crystal X-ray diffraction analysis. The structural model of this phase and two analogs was described as consisting of layers with nickel-main group metal bonds confined from the above by tellurium atoms. The van der Waals gap formed through contacts between the tellurium atoms of neighboring layers is partially occupied by nickel atoms. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1879–1881, October, 2007.     

Effect of Thiourea on the Kinetics of the Hydrogen Evolution Reaction at Iron and the Transport of Hydrogen through a Steel Membrane in Solutions of C<Subscript>2</Subscript>H<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O-HCl

The effect of thiourea (0.5–10 mM) on the kinetics of the hydrogen evolution reaction (HER) at iron and the hydrogen transport through a steel membrane out of ethylene glycol (containing 2 and 10 wt % H₂O) and aqueous solutions containing HCl (0.1–0.99 M) with a constant ionic strength equal to unity is studied in parallel experiments. The presence of 0.5 mM of thiourea in the solutions raises the overvoltage of hydrogen evolution, while a subsequent increase in its concentration does not effect the HER kinetics. The dependence of the flux of hydrogen diffusion through the membrane on the thiourea content passes through a maximum.