Influence of magnetic dilution on the spin transition in the complex of iron(II) nitrate with 4-amino-1,2,4-triazole

Influence of magnetic dilution with Zn^II ions on the spin transition in the iron nitrate complex of 4-amino-1,2,4-triazole (AT) was studied by magnetochemistry, Mössbauer spectroscopy, and IR spectroscopy. In studies of the properties of solid phases of Fe _x Zn _1–x (AT)₃(NO₃)₂ (0.01x0.8), it was demonstrated that magnetic dilution results in a lowered spin transition temperature and an increased share of the high-spin form of the iron(II) complex.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 145–151, November–December, 1993.Translated by L. Chernomorskaya     

Molecular,thermodynamic, and kinetic parameters of iodomethanes and iodomethyl radicals: <Emphasis Type="Italic">ab initio</Emphasis> calculations

The wave functions and enthalpies of formation of the ground states of iodomethanes CH_{4– x} I_x and iodomethyl radicals CH_3–x I_x. (x = 1–3) were calculated ab initio with regard to electron correlation. The geometries of the molecules of these compounds were determined, as well as the normal mode frequencies and other parameters, which were used for calculating the thermodynamic functions in the 0–1500 K range. These functions were used for calculating the constants of the CH_4–x I_x CH_4–x I _x–1 + I and CH_4–x I_x + I CH_{4– x} I _x–1 + I₂ equilibria, which, in turn, were used for calculating the corresponding rate constants in the high concentration limit.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1812–1822.Original Russian Text Copyright © 2004 by Dymov, Skorobogatov, Tschuikow-Roux.This revised version was published online in April 2005 with a corrected cover date.     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.     

On the behavior of the selective oxidation by LiNiO2: Oxidative coupling of methane

The mobility of lattice oxygen and the fine structure of Li_xNi_2–xO₂ (0 x 1.0) were investigated by thermogravimetric analysis and extended X-ray absorption fine structure, respectively. It was proven that the lattice oxygen of LiNiO₂ was mobilizable under reductive and oxidative atmosphere at 1033 K. The Ni–O bond lengths in NiO₆ slabs markedly changed at around x = 0.65. The results were in good agreement with the dependence of the selectivity for the OCM reaction on Li_xNi_2–xO₂ catalysts. It was suggested from these data that the formation of active lattice oxygen species in LiNiO₂ should be induced by structural distortion in NiO₆.     

Angular Overlap Studies of Mono-(Aminodiphosphonato)Copper(II) Complexes in Aqueous Solutions

Electronic absorption spectra of copper(II) complexes with iminodimethylenephosphonates R-N(CH₂PO₃H₂)₂ type (L, R-dmp), in aqueous solution have been characterized and quantitatively interpreted. The geometry of species in aqueous solution at pH 7–8 has been assumed on the basis of our previous combination of UV spectrophotometric measurements and ESR spectra, as well as data obtained from potentiometric titration. The ligand-field spectra (d–d transitions) of the [CuL(H₂O)_x]^2– chromophores (where x = 2, 3) have been treated by the angular overlap model (AOM) and C _2v symmetry. Low-symmetry splittings of the broad asymmetric bands in the spectra of solutions at room temperature were resolved by Gaussian analysis. The effect of the and bonding of the tridentate (and tetradentate) ligands (with oxygen-donor and nitrogen-donor ligators) on the central metal ion has been described in the ligand-field framework.     

Phase Transitions in the BaCe1–x Nd x O3–δ System (x = 0–0.15)

Phase transitions in BaCe_{1 – x} Nd _x O_3– (x = 0–0.15) are studied on ceramic samples by dilatometry (at 370–1100 K) and by measuring electroconductivity (at 750–1220 K). Ion transport numbers are measured by an EMF method at 850–1240 K. All measurements are done in dry air (₂ 40 Pa). By treating the obtained temperature dependences of linear expansion with a difference method (difference between first-degree polynomial approximating the dependence and experimental points), the position and the sort of the phase transitions are determined. High-temperature phase transitions are confirmed by measuring the electroconductivity and ion transport numbers. Second-order phase transitions in pure BaCeO₃ are discovered at 480 ± 10, 530 ± 10, 900 ± 10, 1030 ± 20, and 1170 ± 10 K and a first-order transition, at 665 ±10 K. Phase transitions at 900 and 1030 K are discovered for the first time ever.     

Electroconduction of Potassium Orthophosphate Modified with Triple-Charged Cations

Solid electrolytes in the systems K_{3 – 3x} Me _x PO₄ (Me = Sc, Y, In, La, Nd, Gd, Tb) are synthesized. Their phase composition and the temperature and concentration dependences of their electroconductivity are studied. In all the systems there form solid solutions based on K₃PO₄, which have a high potassium cation conductance. The latter is due to the formation of potassium vacancies at substitutions 3K⁺ Me³⁺ and, at lower temperatures, to stabilization of a high-temperature -modification of potassium orthophosphate. The electroconductivity of synthesized solid solutions, which equals (4–7) × 10^–3 and 10^–1 S cm^–1 at 300 and 700°C, is similar to that of solid electrolytes K_{3 – x} P_{1 – x} E _x ^VIO₄ and K_{3 – 4x} E _x ^IVPO₄.     

Van der Waals Gaps in Sm1+x Ba2−x Cu3O y and Their Effect on Superconductivity

We have used electron–positron annihilation to study superconducting cuprates Sm_1+x Ba_2–x Cu₃O _y . We have determined the average radii for oxygen ions in Sm_1+x Ba_2–x Cu₃O _y . Taking into account the ion coordinates and their radii, we have constructed a geometric model for the arrangement of copper and oxygen ions in CuO₂ layers in the [b, c] plane, responsible for the superconductivity. From these data, we have determined the length of the ionic/covalent bonds and the width of the interionic gaps. We have established the effect of the features of the atomic structure of Sm_1+x Ba_2–x Cu₃O _y on the superconducting transition temperature T _c and we have shown that T _c increases as X inceases.     

Reduction of nitrogen oxides with ammonia over complex vanadium and chromium oxides

Catalytic properties of -Al₂O₃ -supported complex vanadium and chromium oxides V_2–x Cr _x O_5– (0 < × s 1.3), amorphous to X-rays, in the reduction of nitrogen oxides with ammonia were studied. Vanadium exists in these catalysts mostly in a pentavalent state and chromium exists as Cr³⁺ and Cr⁶⁺. As the content of chromium in the catalysts increases, the optimal temperature of the process decreases, and the degree of conversion of nitrogen oxides increases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–342, February, 1996.     

Types of Inorganic Fluorocarbon Polymer Materials and Structure–Property Correlation Problems

The paper reviews published data on the structure and composition of two large classes of inorganic polymer fluorocarbon materials (IP FCMs), including hightemperature (HT) and lowtemperature (LT) modifications of graphite fluorides and fluorographitelike compounds CF _x (x = 0.5 – 1.12$) and CF_1+y (y = 0.08 – 1.33$) and intercalated fluorographite compounds (IFGCs) based on C _x F (x < 2) matrices. According to Xray diffraction data, C1s and F1s Xray photoelectron spectroscopy (XPS), ¹³C and ¹⁹F NMR, CK and FK Xray spectroscopy, and IR and Raman spectroscopy, as well as MNDO calculations, the structure of monolayers and the properties of IP FCMs of C₂F – CF_1+y composition depend on the combination of C(sp ³) – F fragments bonded to the sp ² fragments of the starting carbon matrices. The structure of hightemperature CF_1+y is specified by the presence of structurally isolated external and internal C(sp ³)F₂ groups located on the boundaries of C(sp ³) – F skeleton monolayers and in the holes of their nanostructures, respectively. The enthalpy of formation of HT FCMs does not depend on the type of starting carbon material and is linearly proportional to the F/C atomic ratio; C(sp ³)F and C(sp ³)F₂ groups are chemically indistinguishable in HT FCMs. Six models for the structure of C₂F and C₄F monolayers in LT FCMs are considered. The best agreement with spectroscopy and MNDO data is obtained using modified Yudanov–Gornostaev's model for C₂F, in which alternating rows of graphitelike sp ² carbon fragments coexist with rows of bonded perfluorocyclohexane sp ³ cells. For lowtemperature C₂₄F–C₂F, electric conductivity and C1s and F1s XPS data are generalized and composition–property diagrams are constructed. In this case, the conductivity, C1s and F1s XPS, and the interplanar distances in monolayers are explained using the concept of planarity of C _x F monolayers and the ensuing ideas of semiionic and semicovalent C=F bonds. For C₄F · yA–C₂F · zA compositions, ¹³C and ¹⁹F NMR data, C1s and F1s XPS, and IR data are accounted for by the predominant sp ³ nature of the structureforming C=F bonds.     

Fluoride-conducting Electrolytes Based on Doped Oxyfluorides Pb1 – xAlxF2 + x–2yOy

Employing materials with fast transport of fluoride ions in chemical power sources and gas sensors requires synthesizing new materials with a wide range of electric properties. High conductivity of -PbF₂can be provided by introducing trivalent ions, which create excess concentration of fluoride ions in -PbF₂. Experimental data on the ionic conductivity of Pb_{1 – x} M _x F_{2 + x} , where M is In, Sb, or Bi, are presented in [1–3]. For the first time brief information about high ionic conductivity of doped Pb_{1 – x} Al _x F_{2 + x– 2y} O _y was reported in [4]. Here, we study in greater detail ionic conduction of neat Pb_{1 – x} Al _x F_{2 + x– 2y} O _y and that doped with fluorides of transition metals Zn, Cu, Ni, Co, Mn, Cr, V, or Ti in the temperature range 272–473 K.     

Electroconductivity of Potassium Orthophosphate Modified by Four-Charged Cations

Solid solutions based on K₃PO₄ in systems K_{3 – 4x} E" _x PO₄ (E" = Si, Ti, Ge, Zr, Sn, Hf, Ce) are synthesized. The crystal structure, thermal behavior, and electroconduction of the synthesized solutions is studied. The narrowest single-phase regions take place in the systems where E" = Si, Ge (x 0.025), and the widest, in the system with Zr (x 0.125, at 700°C). Introducing Ti or Sn additives (x 0.05) and minimum quantities of Zr, Hf, or Ce (x = 0.025) into potassium orthophosphate leads to stabilization of highly-conductive -modification of K₃PO₄ at room temperature. Maximum values of potassium-cation conduction in all the systems studied correspond to regions of single-phase solid solutions based on K₃PO₄. The maximum electroconductivity (0.005 S cm^–1 at 300°C, 0.1 S cm^–1 at 700°C) and the smallest activation energies (32–35 kJ mol^–1) take place in the systems with Zr and Hf.     

Determination of Nitrogen in Silicon Carbide by Secondary Ion Mass Spectrometry

The emission of atomic and complex nitrogen ions, which are the main impurity determining the n type conduction of silicon carbide, is investigated. It is shown that, among all the secondary ions of the C _x N and Si _x N kind (x = 0, 1, 2, 3), the ²⁶(CN)^– fragment exhibits the highest ion yield. The use of an ion peak with a specified mass as an analytical signal provides a detection limit for nitrogen in SiC at a level of 10¹⁶ cm^–3. This result is attained in measurements at high mass resolution (M/M = 7500, interference peak ²⁶(¹³C₂)^–).     

Structural Features of Grafted Phosphates in Mesopores of Si-MCM-41 and Ti,Si-MCM-41 Molecular Sieves

We have used ³¹P NMR (MAS) and IR spectroscopy and also chemical analysis to show that when Si- and Ti,Si-MCM-41 mesoporous molecular sieves are treated with phosphorus oxychloride, surface-anchored silicophosphate and titanophosphate compounds are formed of the type (Si—O) _x —{PO(OH)_3–x } and (Ti—O) _x —{PO(OH)_3–x } (x = 1, 2), and also compounds with the structure of titanium hydrophosphate and pyrophosphate.     

Electroconductivity,Nature of Conduction,Thermodynamic Stability of the BaPr1 –xYxO3 – αCeramics

The electroconductivity and the nature of conduction of vacuum-dense ceramics BaPr_{1 – x} Y _x O_{3 –} (x= 0.05–0.15) is studied at temperatures of 373 to 985°C, of 2.1 × 10⁴to 10^–11Pa, and of 40 to 2400 Pa. The coefficient of linear thermal expansion is measured. The ceramics have a perovskite structure and are practically p-type semiconductors with a maximum conductivity of 0.26 S cm^–1at x= 0.10 and 800°C, in air. The share of ionic (proton) conductivity of the ceramics does not exceed 0.2–0.4%. The conductivity is weakly dependent on the air humidity. In a hydrogen-containing atmosphere, the ceramics undergoes reduction with destruction. Boundaries of thermodynamic stability of BaPr_0.9Y_0.1O_{3 –} at 500–900°C are determined.     

Crystal Structures of Two New Holmium Polysulfides in the Series of Rare-Earth Polychalcogenides

The crystal structures of two polysulfide phases HoS_1.885(5) (I) and HoS_1.863(8) (II) were determined; the integer stoichiometric ratio was found to be Ho₈S₁₅. The data were collected on an Enraf-Nonius CAD-4 automatic diffractometer using the standard procedure (MoK, graphite monochromator, an absorption correction applied based on -scan data). Crystal I: space group P4/nmm, a = 3.820(1), c = 7.840(3) , V = 114.40(6) ³, Z = 2 for the composition HoS_1.885(5), d _calc = 6.542 g/cm³, R = 0.0520 for 184 unique reflections with I_hkl > 2 _I; crystal II: space group P2₁/m, a = 10.961(2), b = 11.465(2), c = 10.984(2) , = 91.27(3)°, V = 1380.0(4) ³, Z = 24 for the composition HoS_1.863(8), d _calc = 6.486 g/cm³, R = 0.0596 for 5354 unique reflections with I_hkl > 2 _I. In both compounds, the Ho atoms are surrounded by 9 (8+1 for three atoms in II) S atoms forming monocapped square antiprisms. The Ho–S distances vary from 2.717 to 3.067 irrespective of the type of ion [S^2– or (S₂)^2–]; the maximal distance to the atoms completing the coordination is 3.684 . The compounds have PbFCl type structures composed of ...(S₂)^2–...Ho³⁺...S^2–...S^2–...Ho³⁺...(S₂)^2–... layer packets differently oriented in space relative to the unit cell axes. The S^2–...S^2– and S^2–...(S₂)^2– interlayer distances are mostly shorter than the sum of the ionic radii and vary within the limits of 3.331-3.558 and 3.029-3.784 for the first and second types, respectively. For I, the calculated site occupancies and densities are given depending on the composition Ho-S_2-x (x = 0.25-0); for II, the most probable formulas of rational compositions in the same range of x are presented.     

Stoichiometric ratio and doping effects on the thermal properties of sodium potassium sulphate crystals

The influence of stoichiometric ratio on the phase transition of sodium potassium sulphate (Na_xK_1–x)₂SO₄ crystals is investigated in the temperature range 300–500 K. The stoichiometric ratiox is chosen to bex=0.2, 0.3, 0.4, 0.8 and 0.9. The study has been carried out by using differential scanning calorimetry, DSC technique. The value of the specific heat,C _p, at the transition temperature,T _c , increases asx is increased up tox=0.4 and then decreases for higher values ofx. The change in the specific heat, C _p, is following a relation of the form C _p C _p (T–T _c /T _c )^– with = 0.12 which is in a fair agreement with the 3d Ising model. Insertion of Cu²⁺ ions into the lattice of (Na_xK_1–x)₂SO₄ crystals leads to a multiple peak in the temperature dependence ofC _p. The results are discussed from thermodynamical point of view.We would like to thank Prof. E. F. El-Wahidy, Prof. of Solid State Physics and Head of Physics Department, Faculty of Science, Alexandria University, for his interest and support of this work.     

Investigations in the ternary system Ti-Mo-N by means of EPMA and XRD

Arc-melted ternary Ti-Mo-N alloys were heat treated at 1423 K in order to evaluate the compositions of the equilibrium phases. The composition of the bcc phase-Ti _x Mo_1–x with respect to Mo and Ti was determined by electron probe microanalysis (EPMA) and lattice parameter measurements (XRD). In order to avoid the effects of plastic deformation caused by powdering the ductile-Ti _x Mo_1–x alloys, the lattice parameter measurements were carried out on small particles of the compact samples using Debye-Scherrer cameras. The EPMA and XRD results agree within the expected range of accuracy. Apparently the solubility of nitrogen in-Ti _x Mo_1–x is low and does not perceptibly affect EPMA and XRD results. The relationship between the lattice parameter and the nitrogen content of-TiN_1–x was applied to determine the composition of-TiN_1–x in equilibrium with-Ti_xMo_1-x No solid solubility of Mo in TiN_1–x could be detected. The tie lines at 1423 K between the two phases were established.     

Conduction and Transport Numbers in Metacomposites MeWO<Subscript>4</Subscript> ⋅ WO<Subscript>3</Subscript> (Me = Ca,Sr, Ba)

The conduction and transport numbers of charge carriers for composites in the systems MeWO₄-WO₃ (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO₄ ⋅ xWO₃ is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α _MeW-s ≤ ) and a higher mobility with respect to MeWO₄ and WO₃. The discovered anomalies of dependences (T) and partial dependences , σ_el(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Photochemistry of benzimidazolocyanine dyes in solvents of different polarity

The effect of ion pair formation on the kinetics of the decay of the photoisomers and triplet states of cationic benzimidazolocyanine dyes is studied by flash photolysis. An increase in the rate constant of the reversecis-trans isomerization of the photoisomers is observed when ion pairs are formed (in nonpolar solvents). In the case of benzimidazolocyanine dyes with the I^– anion, ion-pair formation causes an increase in the rate constant of decay of the triplet state. Acceleration of S₁ S₀ internal conversion is discovered for the dyes with I^–1 Translated fromIvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 507–512, March, 1993.