On the existence of phases with a structure of NaZr2(PO4)3 in series of binary orthophosphates with different alkaline element to zirconium ratios

Complex phosphates M_xZr_2.25–0.25x(PO₄)₃, where M=Li, Na,K, Rb or Cs and x may be an integer or fraction from 0 to 9, have been synthesized, and their structure has been investigated. The concentration and temperature ranges of stability of the phosphate phases NaZr₂(PO₄)₃ have been found. The influence of the method for the synthesis of these phases and of the annealing temperature on their crystal properties is studied. It was found that the structure of NaZr₂(PO₄)₃ [NZP] exists in the above phosphate series when 0≤x≤5 for Na and K, 0≤x≤3 for Rb, and 0≤x≤1 for Cs. N. I. Lobachevskii Nizhnii Novgorod State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1104–1113, November–December, 1996. Translated by L. Smolina     

Modeling of Aqueous 3–1 Rare Earth Electrolytes and Their Mixtures to Very High Concentrations

A simple modification to the Pitzer ion–interaction model has been presented for osmotic and activity coefficients of aqueous solutions of highly soluble and highly unsymmetrical electrolytes and their mixtures. The equations extending to the C⁽³⁾ parameter enable the literature osmotic and activity coefficients of aqueous rare earth nitrates, perchlorates and chlorides at 298.15 K to be represented accurately from infinite dilution to maximum saturation or supersaturation concentrations available. The ionic interactions have also been investigated from the isopiestic measurements on aqueous mixtures Y(NO₃)₃–La(NO₃)₃, Y(NO₃)₃–Pr(NO₃)₃, Y(NO₃)₃–Nd(NO₃)₃, La(NO₃)₃–Pr(NO₃)₃, La(NO₃)₃–Nd(NO₃)₃ and Pr(NO₃)₃–Nd(NO₃)₃ at 298.15 K to near saturation, and the simple modification can represent the new measurements within experimental uncertainty over the full concentration range. In addition, the Zdanovskii-Stokes-Robinson model or partial ideal solution model is obeyed by all the mixtures within isopiestic accuracy, which is consistent with the nature of rare earth elements.     

Structure and dielectric properties of 80%Pb(Zn1/3Nb2/3)O3–20%PbTiO3 thin films prepared by modified sol–gel process

80%Pb(Zn_1/3Nb_2/3)O₃–20%PbTiO₃ (PZN–PT) thin films have been prepared on Pt/Ti/SiO₂/Si substrates using a modified sol–gel method. In our method, niobium pentaoxide is used as a substitution instead of niobium ethoxide which is moisture-sensitivity and much more expensive. Microstructure and electrical properties of PZN–PT thin films have been investigated. X-ray diffraction analysis shows that proper annealing temperature of PZN–PT thin films is 600 °C. The PZN–PT thin films annealed at 600 °C are polycrystalline with (111)-preferential orientations. Field-emissiom scanning electron microscope analysis revealed PZN–PT thin films possess well-defined and crack-free microstructure. The thickness of thin films is 290 nm. The Pt/PZN–PT/Pt capacitors have been fabricated and it presents ferroelectric nature. The remanent polarization (Pr), spontaneous polarization (Ps), and the coercive electric field (Ec) are 8.71 μC/cm², 43.06 μC/cm², and 109 kV/cm at 1 MHz, respectively. The dielectric constant (ε_r) and the dissipation factor (tan δ) are about 500.3 and 0.1 at 1 kHz, respectively.     

Role of CH, CH3, and OH Radicals in Organic Compound Decomposition by Water Plasmas

Decomposition of acetone, methanol, ethanol, and glycerine by water plasmas at atmospheric pressure has been investigated using a direct current discharge. At torch powers of 910–1,050 W and organic compound concentrations of 1–10 mol%, the decomposition rate of methanol and glycerine was over 99%, while those of acetone and ethanol was 95.4–99%. The concentrations of H₂ obtained were 60–80% in the effluent gas for any compounds by pyrolysis. Based on the experimental results, the decomposition mechanism of organic compounds in water plasmas was proposed and the roles of intermediate species such as CH, CH₃, and OH have been investigated; CH radical generated from organic compounds decomposition was easily oxidized to form CO; incomplete oxidation of CH₃ leads to C₂H₂ generation as well as soot formation; and negligible amount of soot observed from glycerine decomposition even at high concentration indicated that oxidation of CH_×(×:1–3) was enhanced by OH radical.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

Photocatalytic degradation of Orange II by titania addition to sol–gel glasses

Glasses on SiO₂–CaO–ZnO–B₂O₃–K₂O–Al₂O₃ oxide system modified by addition of titania (0, 3, 5, 12, and 20% w) have been prepared by sol–gel method. The obtained gels were aged, dried and fired at 600 °C/1 h in order to stabilise the glass. The resulting fired powders were characterised by UV–Vis–NIR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). Their photocatalytic capacity on the degradation of Orange II dye has been studied. The XRD and TEM studies indicate that system becomes amorphous with a nanostructured microstructure. From UV–Vis–NIR results the band gap calculated is around 3.5 eV for all modified glasses. Photoactivity of powders depends on amount of titania in glass composition and the specific surface area of prepared samples. The sample with highest surface area and lowest addition of titania (3% w sample) shows similar activity than commercial anatase used as reference.     

Surface structure of silica gel reacted with 3-mercaptopropyltriethoxysilane and 3-aminopropyltriethoxysilane: formation of the S–S bridge structure and its characterization by Raman scattering and diffuse reflectance Fourier transform spectroscopic studies

 Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH₂SSCH₂ segment, in addition to the SH and C–S stretch modes of the CH₂SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel, a specific conformer is stabilized about the CH₂SSCH₂ segment. Received: 1 May 2001 Accepted: 16 June 2001     

The effects of gamma irradiation on non-isothermal crystallization kinetics and microhardness of the Li<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass–ceramic

The effects of gamma irradiation on crystallization kinetics and microhardness properties of the Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramic sample have been investigated. The glass–ceramic was irradiated to γ-source ⁶⁰Co of 0.7 MGy. The crystallization kinetics of the irradiated and non-irradiated samples were characterized using differential scanning calorimetry. The crystallization kinetics and microhardness properties of the glass–ceramic changed the gamma irradiation, and the high dose of gamma irradiation affects significantly the crystallization kinetics and microhardness properties of the Li₂O–Al₂O₃–SiO₂ glass–ceramic sample.     

Indium selenide thin film preparation by sol–gel technique

Preparation and characterization of In–Se compound thin films prepared by sol–gel methods on glass substrate have been studied. X-ray diffraction analyses and optical transmission spectrum of In–Se compound thin film samples show that the fabricated sol–gel In–Se thin films features formed mainly as an In₂Se₃ crystal structure. From transmission spectra of In–Se thin films band gap energy were estimated approximately as ∼1.24 eV.     

Metamagnetic DyAlO<Subscript>3</Subscript> nanoparticles with very low magnetic moment

Nanocrystalline dysprosium monoaluminate (DyAlO₃) has been synthesized by modified sol–gel method after sintering the precursor gel at 950 °C. The micro-structural features have been verified by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy. The XRD pattern confirms the formation of single-phase DyAlO₃; the average size of the nanoparticles is 50 nm. X-Ray photoelectron spectroscopy has been used to study the chemical composition and bonding in the samples. The binding energies of core-level electrons in Dy, Al and O in DyAlO₃ nanopowder have been found slightly shifted compared to the respective values of the same elements. Both AC and DC magnetic susceptibilities have been measured in the temperature range 2–300 K. Unusually low effective magnetic moment of Dy³⁺, μ_eff = 0.38, has been derived from the inverse magnetic susceptibility–temperature plot between 4 and 252 K. The Nèel temperature, T_N = 3.920 K and exchange interaction constant J/k = −1.74 K, have been also determined.     

A study of HPLC separation and spectrophotometric and voltammetric detection of 4′-substituted derivatives of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene

 Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazo-benzene derivatives substituted in the position 4′ (4′-R-CHAAB, where R=–H, –CH₃, –OCH₃, –Cl, –COCH₃, –NO₂ and –NHCOCH₃) using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of 0.01 mol/L NaH₂PO₄ at pH 4 with methanol (1+1), 0.01 mol/L NaH₂PO₄ at pH 2 with acetonitrile (1+1) or 1% aqueous acetic acid with methanol (4+6). UV photometry is the most universal detection technique and yields limits of detection around 10^-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for –COCH₃ derivatives and higher limits of detection for –NO₂ and –NHCOCH₃ derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits of detection one order of magnitude lower than those obtained UV photometrically. Received: 27 June 1996/Revised: 25 October 1996/Accepted: 3 November 1996     

ETS-10 synthesized from gels with dodecyltrimethylammonium bromide

The aim of this paper is to define the characteristics of crystalline phase ETS-10 obtained from gel with dodecyltrimethylammonium bromide, as an organic template. ETS-10 zeolites has been synthesised under hydrothermal conditions from gels of composition 5Na₂O–3KF–TiO₂–6.4HCl– xC₁₂TMAB –7.45SiO₂–197.5H₂O (where x=0.0, 0.25, 0.55, 1.0 and 1.5) with dodecyltrimethylammonium bromide. The crystalline phases synthesised with organic salt have an exothermal peak at ca. 360°C, due to the degradation of organic entrapped in the porous structure. Physical-chemical properties of C₁₂TMAB -ETS-10 are studied by XRD, SEM and thermal analyses.     

Accessing HgSe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">1−x</Emphasis></Subscript> Nanoparticles Using the Single-Source Reagent Me<Subscript>3</Subscript>Si–SeS–SiMe<Subscript>3</Subscript>

Mercury-selenosulfide (HgSe _x S _1-x ) nanoparticles have been synthesized using the single-source reagent Me₃Si–SeS–SiMe₃. The reagent distributes Se²⁻ and S²⁻ to the metal core as the reaction between Me₃Si–SeS–SiMe₃ and mercury acetate occurs via a redox pathway, ultimately giving rise to Se–S bond cleavage. Particles are characterized by EDX, TEM and powder X-ray diffraction analysis in conjunction with UV–Visible absorption spectroscopy. Dedicated to Prof. Dr. Dieter Fenske on the occasion of his 65th birthday.     

Composition and structure refinement of superconducting crystals Y1? x Tb x Ba2Cu3O6+δ ( x = 0.10; δ = 0.75)

Crystals of Y_0.90Tb_0.10Ba₂Cu₃O_6.75 have been prepared by spontaneous crystallization from slowly cooled non-stoichiometric melt of the system Y-Tb-Ba-Cu-O. Average size of platelet crystals having mirror surface is 2×2, the largest — 8×9 mm with thickness 0.1–0.2 mm. The crystals have been characterized by powder X-ray diffraction and electron microprobe analysis. Tetragonal symmetry of the crystals has been determined by X-ray diffraction. Magnetic susceptibility measurements have revealed that the crystals manifest transition to superconducting state without additional annealing (T _c = 60 K). Structures and compositions — Y/Tb ratio (σ = 0.01) and oxygen content (σ = 0.04) — have been refined for two single crystals. Possibility of rhombic distortion of the tetragonal symmetry is discussed. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 6, pp. 1101–1107, November–December, 2008. Original Russian Text Copyright ? 2008 by L. P. Kozeeva, N. V. Podberezskaya, N. V. Kuratieva, M. Yu. Kamaneva, and A. G. Blinov     

The effect of CH<Subscript>3</Subscript>, F and NO<Subscript>2</Subscript> substituents on the individual hydrogen bond energies in the adenine–thymine and guanine–cytosine base pairs

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The electron withdrawing (EW) substituents (F and NO₂) increase the total binding energy (ΔE) of X–G–C derivatives and the electron donating (ED) substituent (CH₃) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH₃ in the 1 position and F in the 5 position, which in both cases the ΔE value decreases negligibly small. With minor exceptions (X=8–CH₃, 8–F, and 9–NO₂), both ED and EW substituents increase slightly the ΔE values of X–A–T derivatives. The individual HB energies (∆E _HBs) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the role of atoms entered H-bonding. The remarkable change is observed for NO₂ substituted derivative in each case.     

Thermal stability and crystallization kinetics in superionic glasses using electrical conductivity–temperature cycles

The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag₂O–V₂O₅–MoO₃ superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag⁺ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T _g) followed by a drastic fall at crystallization (T _c). The temperature corresponding to maximum rate of crystallization (T _p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T _g, T _p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E _s, crystallization E _c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable within experimental error.     

Mechanism of formation of 3-methyl derivatives of imidazo[2,1-<Emphasis Type="Italic">b</Emphasis>]thiazoles and their benzo analogs in the reactions of 2-mercaptoimidazole and 2-mercaptobenzimidazole with 1,3-dichloroacetone under phase-transfer catalysis conditions

The mechanism of the unexpected formation of 3-methyl derivatives of imidazo[2,1-b]thiazoles in the system 2-mercaptoimidazole–1,3-dichloroacetone–solid K₂CO₃–solid KI–18-crown-6–toluene has been studied. The structure of 3-methyl[1,3]thiazolo[3,2-a]benzimidazole has been confirmed using X-ray structural analysis.     

Thermal degradation and smoke suspension of cotton cellulose modified with THPC and its lanthanide metal complexes

Complexes of cell–THPC–urea–ADP with transition metal ion Co²⁺ and lanthanide metal ions such as La³⁺, Ce⁴⁺, Nd³⁺ and Sm³⁺ have been prepared. The thermal behavior and smoke suspension of the samples are determined by TG, DTA, DTG and cone calorimetry. The activation energies for the second stage of thermal degradation have been obtained by following Broido equation. Experimental data show that for the complexes of cell–THPC–urea–ADP with the metal ions, the activation energies and thermal decomposition temperatures are higher than those of cell–THPC–urea–ADP, which shows these metal ions can increase the thermal stability of cell–THPC–urea–ADP. Moreover, these lanthanide metal ions can more increase thermal stability of samples than do the transition metal ion Co²⁺. The cone calorimetry data indicate that the lanthanide metal ions, similar to transition metal Co²⁺, greatly decrease the smoke, CO and CO₂ generation of cell–THPC–urea–ADP, which can be used as smoke suppressants.     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.