Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 ? x ? ySrxLayMnO3 ? δ

The content of oxygen in Ca_{0.6 − y} Sr_0.4La _y MnO_{3 − δ}, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10⁻⁴ to 1 atm. The results were used to calculate the partial molar enthalpy, Δ$ \bar H $ \bar H _O(δ), and entropy, Δ$ \bar S $ \bar S _O(δ), of oxygen in manganites. Changes in the Δ$ \bar H $ \bar H _O(δ) and Δ$ \bar S $ \bar S _O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca_0.6Sr_0.4MnO_{3 − δ} matrix.     

Volumetric properties of the water-ethylene glycol mixtures in the temperature range 278–333.15 K at atmospheric pressure

Density of the water-ethylene glycol binary mixtures was measured in the entire range of compositions in the temperature range 278–333.15 K (6 values) at atmospheric pressure using a vibration densimeter. Mixtures with low concentrations of ethylene glycol were studied at 15 temperatures in the range of 274–333.15 K. Excess molar volumes V _m ^E , the partial molar volumes of water -V ₁ and ethylene glycol, -V ₂, the coefficients of thermal volume expansion α of the mixture, the partial molar volume coefficients of thermal expansion of water $ \bar V_1 $ \bar V_1 and ethylene $ \bar V_2 $ \bar V_2 were calculated. Excess molar volumes were described using the Redlich-Kister equation. The density ρ of the mixture was found to increase with the increasing ethylene glycol concentration at all temperatures, but at low content of ethylene glycol the dependence ρ = f(T) of the mixture at ∼276.5 K passed through a maximum. The coefficient α increases sharply in the composition range 0 < x < 0.2, in the range 0.5 < x <1 remains almost unchanged, and at T > 277 K is positive for all compositions. The dependences $ \bar \alpha _1 $ \bar \alpha _1 = f (x) and $ \bar \alpha _2 $ \bar \alpha _2 = f (x) are complex in whole temperature range and are characterized by the presence of an extremum. V _m ^E values are negative at all temperatures, and upon increase in the temperature the deviation from ideality decreases (x is the mole fraction of ethylene glycol).     

The compressibility of water-dimethyl sulfoxide mixtures over the temperature and pressure ranges 278–323.15 K and 1–1000 bar

The compressibility coefficients of water-dimethyl sulfoxide (DMSO) binary liquid mixtures were measured over the temperature range 278–323.15 K at pressures from atmospheric to 1000 bar. At these state parameters, the partial molar volumes and partial molar compressibility coefficients $ \bar k_1 $ \bar k_1 and $ \bar k_2 $ \bar k_2 of water and DMSO were calculated. The dependences of the compressibility coefficients of mixtures on mixture composition passed a minimum. The minimum shifted to lower DMSO concentrations as the temperature increased. The dependences contained the inversion region where the k value was independent of pressure. The limiting molar partial compressibility coefficient of DMSO $ \bar k_2 $ \bar k_2 was negative at 278.15 K and increased as the temperature grew.     

Molecular-mass-distribution of oligomers in the products of tetrafluoroethylene telomerization in various solvents

The possibility of using differential thermogravimetry (DTG) for determination of the molecularmass-distribution (MMD) of oligomers in polymerization products has been experimentally and theoretically substantiated. The technique is based on the assumptions that the increase in the boiling temperature of oligomers with the increasing chain length is described by the additivity rule and the shape of DTG curves obeys the equation of mass transfer in the stationary convective flow created by evaporation. The results have been confirmed by gel-permeation chromatography and ¹⁹F NMR data. It has been shown that the chain length of oligomers produced via tetrafluoroethylene (TFE) telomerization in carbon tetrachloride, chloroform, acetone, and ethyl acetate reaches about 20–25 C₂F₄ units at an initial TFE concentration of C ₀ ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C ₀ and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C ₀. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers.     

Dependence of molecular polarizability on the orientational order in nematic liquid crystals

The dispersion dependences of refractive indices in the visible range were used to obtain experimental values of the Lorentz tensor components L _j and the mean molecular polarizability $ \bar \gamma $ \bar \gamma for five nematic liquid crystals belonging to two homological series. The dependence of L _j components on the homologue number, mesophase temperature, birefringence value, and the orientational order of molecules in the nematic phase and upon a nematic-smectic A phase transition was revealed. The effect of the isotropization of the Lorentz tensors and the local field tensor with decreasing birefringence and molecular polarizability anisotropy Δγ was confirmed. The quadratic dependence $ \bar \gamma $ \bar \gamma (S) on the molecular orientational order parameter S in the nematic phase was found. It was invariant with respect to the nematic-smectic A transition. The dependences $ \bar \gamma $ \bar \gamma (S) and Δγ(S) are explained within molecular statistical theory as consequences of the correlation between orientational and conformational degrees of freedom of molecules. These conformational degrees of freedom are related to the internal rotation of molecular fragments, which affects the electronic conjugation of the fragments and the oscillator strengths of molecular transitions.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Heat capacity and density of methylpyrrolidone solutions of sodium and potassium perchlorates at different concentrations and 298.15 K

The heat capacity and density of solutions of sodium and potassium perchlorates in N-methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The standard partial molar heat capacities $ \bar C_{p2}^ \circ $ \bar C_{p2}^ \circ and volumes $ \bar V_2^ \circ $ \bar V_2^ \circ of NaClO₄ and KClO₄ in MP were calculated. The standard heat capacities $ \bar C_{pi}^ \circ $ \bar C_{pi}^ \circ and volumes $ \bar V_i^ \circ $ \bar V_i^ \circ of the perchlorate ion in an MP solution at 298.15 K were determined. The results are discussed with allowance for the specifics of solvation in the solutions of the salts under study. The coordination number of the ClO₄⁻ ion in an MP solution at 298.15 K was calculated.     

Coordination polymers based on [Re6Se8(CN)6]4? cluster anion, lanthanide cations, and tetraatomic alcohol erythritol

By the interaction of aqueous solutions of salts of the [Re₆Se₈(CN)₆]⁴⁻ cluster anion with salts of Nd(III), Tb(III), and Yb(III) lanthanides in the presence of tetraatomic alcohol erythritol (butane-1,2R,3S,4-tetraol) three new compounds are obtained: K[Nd(C₄H₁₀O₄)(H₂O)₄{Re₆Se₈(CN)₆}]·4H₂O (P $ \bar 1 $ \bar 1 space group, a = 11.544 ?, b = 13.643 ?, c = 13.838 ?, α = 111.97°, β = 108.08°, γ = 90.08°) (1); [{Yb₂(C₄H₉O₄)₂ × (H₂O)₂}{Re₆Se₈(CN)₆}]·5H₂O (P $ \bar 1 $ \bar 1 space group, a = 10.308 ?, b = 10.505 ?, c = 11.154 ?, α = 88.21°, β = 81.83°, γ = 78.50°) (2); [{Tb₂(C₄H₉O₄)₂(C₄H₁₀O₄)}{Re₆Se₈(CN)₆}]·4H₂O (P $ \bar 1 $ \bar 1 space group, a = 10.002 ?, b = 10.276 ?, c = 11.762 ?, α = 91.32°, β = 104.01°, γ = 106.02°) (3). The structures of these compounds are the coordination polymers (chain (2) and grids (1 and 3)) with different coordination modes of erythritol to the lanthanide cations.     

Deformation C-S and S=O bond polarizations in dimethyl sulfoxide

The data on the permittivities of crystalline 1,4-dithiane and 1,4-dithiane-1,4-dioxide were used to calculate the molar deformation polarizations of the C-S (P _{∞, C-S} = 3.84 cm³/mol) and S$ \underline \ldots $ \underline \ldots O ($ P_{\infty ,S\underline \ldots O} $ P_{\infty ,S\underline \ldots O} = 4.34 cm³/mol) bonds within the framework of the additive scheme suggested by Levin. These data were used to calculate the deformation permittivity of dimethylsulfoxide (DMSO) at 298.15 K, ɛ_{∞, DMSO} = 2.36, and the dipole correlation factor of pure DMSO, g ^dip = 1.055.     

Subsolidus phase relations in the Na2MoO4-CoMoO4-Cr2(MoO4)3 system

Triple molybdate NaCoCr(MoO₄)₃, a phase of variable composition Na₂MoO₄-CoMoO₄-Cr₂(MoO₄)₃ (0 ≤ x ≤ 0.5) having nasicon structure (space group R $ \bar 3 $ \bar 3 c), and triple molybdate NaCo₃Cr(MoO₄)₅ crystallizing in triclinic space group P $ \bar 1 $ \bar 1 were synthesized in the subsolidus region of the Na₂MoO₄-CoMoO₄-Cr₂(MoO₄)₃ ternary salt system. Crystal parameters were calculated for the newly synthesized molybdates and phases. The vibration spectra of Na_{1 − x} Co_{1 − x} Cr_{1 + x} (MoO₄)₃ and electrophysical properties were studied. Upon Na + Co → Cr(III) substitution, chromium cations are distributed to cobalt sites and additional vacancies are generated in the sodium sublattice.     

Synthesis and study of the variable-composition phase Na1?xCo1?xFe1+x(MoO4)3, 0 ≤ x ≤ 0.4, with nasicon structure

The synthesis conditions for variable-composition phase Na_1−x Co_1−x Fe_1+x (MoO₄)₃, 0 ≤ x ≤ 0.4, crystallizing in the nasicon structure type (R $ \bar 3 $ \bar 3 c) were examined. For this phase, the crystallographic parameters were calculated, vibrational spectra were interpreted, and temperature dependence of electrical conductivity, dielectric constant, and dielectric loss tangent were examined.     

Crystal structure of a new coordination polymer [LaAg(Pydc)(HPydc)(C2O4)0.5(H2O)2]n (H2Pydc = pyridine-3,5-dicarboxylic acid)

A new 3D coordination polymer, [LaAg(Pydc)(HPydc)(C₂O₄)_0.5(H₂O)₂] _n (I) (H₂Pydc = pyridine-3,5-dicarboxylic acid), has been hydrothermally synthesized and characterized by elemental analyses and single crystal X-ray diffraction. The X-ray diffraction analysis reveals that I (C₁₅H₁₁AgLaN₂O₁₂) crystallizes in triclinic space group P $ \bar 1 $ \bar 1 and features an interesting 3D framework constructed by 2D layers via strong Ag-Ag interactions. Unit cell parameters for I (n = 1): a = 7.749(2), b = 8.316(1), c = 14.239(3) ?, α = 97.64(2)°, β = 100.12(2)°, γ = 94.37(2)°, and Z = 2.     

Volume properties of a ternary system: Water-urea-amino acid. Dilute and concentrated solutions

Partial molar volumes $ \bar V_U^0 $ \bar V_U^0 of amino acids in an aqueous urea solution are studied. For a saturated urea solution $ \bar V_U^0 $ \bar V_U^0 equals the molar volume of the amino acid, therefore, in the saturated solution, the amino acid dissolves without changing the system volume. Hydrophobic effects are manifested in the volumetric characteristics only in dilute (<1 mol/kg) urea solutions. Within a three-layer hydration model, the numbers of amino acid hydration are found. By the example of alanine and leucine, it is shown that their decrease with increasing urea concentration is determined by a zwitterionic moiety and does not depend on the size of the hydrocarbon radical of the amino acid.     

Synthesis and crystal structure of sodium isopolyvanadate [Na2(H2O)8]2H2[V10O28] · 4H2O

The sodium hydrogen oxovanadate [Na₂(H₂O)₈] ₂H₂[V₁₀O₂₈] · 4H₂O was synthesized and studied by TGA, X-ray diffraction, and NMR and IR spectroscopy. The crystals are triclinic, space group P $ \bar 1 $ \bar 1 , a = 8.545(7) ?, b = 10.827(2) ?, c = 11.627(2) ?, α = 105.48(3)°, β = 99.38(3)°, γ = 101.29(3)°, V = 989.9(3) ?³, ρ(calcd) = 2,381 g/cm³, Z= 1.     

Non-isothermal studies on crystallization kinetics of tellurite 20Li<Subscript>2</Subscript>O-80TeO<Subscript>2</Subscript> glass

Structural and thermal properties of the 20Li₂O-80TeO₂ glass were studied using X-ray diffraction analysis and differential scanning calorimetry techniques to understand and control the crystallization process on this glass. The γ-TeO₂, α-TeO₂ and α-Li₂Te₂O₅ phases were identified during the crystallization in this glass. Activation energies and Avrami exponent n were calculated from non-isothermal measurements for glasses with different particle size. The mean values of Avrami exponent were obtained for glasses with 63–75 and 45–63 μm particle sizes such as , but glasses with particle size 38–45 μm and smaller than 38 g,m presented .     

On the theory of oscillating flows in complex liquids

Experiments with highly concentrated suspensions and other complex liquids frequently demonstrate nonmonotonic N- or S-shaped dependences of viscous stress σ on shear rate $ \dot \gamma $ \dot \gamma and strong oscillations of the shear rate at a constant flow-inducing external stress, as well as oscillations of the viscous stress at a constant average shear rate. A phenomenological mathematical model is proposed for oscillating flows according to which oscillations arise when an applied stress (or the average shear rate, depending on the design of an experiment) is in the descending region of the σ-$ \dot \gamma $ \dot \gamma dependence and a complex liquid exhibits pronounced viscoelastic properties.     

Ionic conductivity of sodium silicates with lovozerite-type structure

The ionic conductivity of Na,Zr and Na,Sn silicates of the lovozerite family (Na_{8 − x} H _x ZrSi₆O₁₈ structural type, space group R $ \bar 3 $ \bar 3 m) was studied in the temperature range of 293–800 K using the impedance spectroscopy method (5−5 × 10⁵ Hz). The compositions of the studied compounds were obtained using the method of hydrothermal synthesis in the MO₂-SiO₂-NaOH-H₂O and MO₂-SiO₂-CaO-NaOH-H₂O (M = Zr, Sn) systems at 573–823 K. The samples for electrophysical studies were prepared according to the ceramic technology. It was found that isovalent cation substitutions of Sn⁴⁺ → Zr⁴⁺ in Na₈M⁴⁺Si₆O₁₈ and Na₆CaM⁴⁺Si₆O₁₈ and H⁺ → Na⁺ in Na_{8 − x} H _x ZrSi₆O₁₈ result in an increase in the ionic conductivity by 2–3 orders of magnitude, without affecting the ionic transport activation energy (0.6–0.7 eV). The best electrolytic characteristics are typical for the Na₅H₃ZrSi₆O₁₈ compound, for which the ionic conductivity value is 5 × 10⁻⁴ S/cm at 573 K.     

Growth mechanism and characterization of ZnO nano-tubes synthesized using the hydrothermal-etching method

ZnO nano-tubes (ZNTs) have been successfully synthesized via a simple hydrothermal-etching method, and characterized by X-ray diffraction, field emission scanning electron microscopy and room temperature photoluminescence measurement. The as-synthesized ZNTs have a diameter of 500 nm, wall thickness of 20–30 nm, and length of 5 μm. Intensity of the plane (0002) diffraction peak, compared with that of plane (10$ \bar 1 $ \bar 1 0) of ZNTs, is obviously lower than that of ZnO nano-rods. This phenomenon can be caused by the smaller cross section of plane (0002) of the nano-tubes compared with that of other morphologies. On basis of the morphological analysis, the formation process of nano-tubes can be proposed in two stages: hydrothermal growth and reaction etching process.     

Concentration dependences of the heat capacity of solutions of alkali metal iodides in N-methylpyrrolidone-water mixed solvent at 298.15 K

Heat capacities of solutions of alkali metal iodides (MeI) in N-methylpyrrolidone (MP)-water mixed solvent were measured over the range of compositions. The influence of the composition of the mixed solvent on the heat capacity of MeI-MP-H₂O ternary systems is discussed. Standard partial molar heat capacities $ \bar C_{p_2 }^o $ \bar C_{p_2 }^o (MeI) in the MP-water mixed solvent at 298.15 K are calculated.     

Two octacyanomolybdate(IV)-M(II) (M = Mn,Co) bimetallic assemblies: Crystal structures and magnetic properties

Two cyano-bridged bimetallic complexes {[M₂(H₂O)₄Mo(CN)₈] · 4H₂O} _n [M = Mn (I) and Co (II)] have been synthesized and structurally characterized. The single-crystal X-ray analyses reveal that these two compounds have three-dimensional structures, and cell parameters are similar in a tetragonal system with space group I $ \bar 4 $ \bar 4 . In the both complexes, each [Mo(CN)₈]⁴⁻ building block is linked with M²⁺ [M = Mn and Co] ions through its eight CN ligands. Each M²⁺ center is connected to four Mo units forming a three-dimensional framework. In addition, magnetic studies of these complexes have been presented.