Formation and properties of copper chalcogenides thin films on polymers formed using sodium telluropentathionate

The preparative conditions were optimized to get chalcogens layers on the polymer — polyamide PA surface by sorption at room temperature using sodium telluropentathionate, Na₂TeS₄O₆. Further interaction of chalcogenized dielectric with copper’s (I/II) salt solution leads to the formation of mixed Cu_xS_y-Cu_xTe_y layers. Optical, electrical and surface characteristics of the layers are highly controlled by the deposition parameters. The stoichiometry of these layers was established by UV-Visible and AA spectrometry. Optical absorption (transmittance) experiments show the samples are of high optical quality. The band gaps of thin films were obtained from their optical absorption spectra, which were found in the range of 1.44–2.97 eV. XRD was used in combination with AFM to characterize chalcogenides layers’ structural features. XRD analysis confirmed the formation of mixed copper chalcogenides’ layers in the surface of PA with binary phases such as Cu₂Te, Cu_3.18Te₂, copper telluride, Cu_2.72Te₂, vulcanite, CuTe, anilite, Cu₇S₄ and copper sulfide, Cu_1.8S. The crystallite sizes of thin films calculated by the Scherer formula were found to be in the range of 3.07–13.53 nm for Cu_xS_y crystallites and 4.06–20.79 nm for Cu_xTe_y crystallites. At room temperature an electrical resistance of Cu_xS_y-Cu_xTe_y layers varies from 3.0×10³ kΩ□^?1 to 1.0 kΩ□^?1.      

Comparison of the efficacy of sulfurization agents in decreasing the sheet resistance of polyamide and polyethylene with copper sulfide layers and influence of their compositions

The process of obtaining semiconductive and electrical conductive layers of copper sulfides by the sorption — diffusion method on polymers (polyamide 6 and low density polyethylene) using solutions of potassium pentathionate, K₂S₅O₆, and higher polythionic acids, H₂S _n O₆ (n = 21, 33), was investigated. The layers were characterized for compositional and electrical properties by X-ray diffraction (XRD) analysis and sheet resistance measurements. The thickness of copper sulfides layers on polyamide and polyethylene increased with increasing time of polymer sulfurization and varied from 10 to 43 μm. The variations of the sheet resistance of copper sulfides layers formed on the surface of polymers on sulfurization agent used, the conditions of sulfurization, chemical and phase composition of the obtained layers were established. Sheet resistance of copper sulfides layers decreases with increasing time of the duration of sulfurization and the number of sulfur atoms in the polythionate anion. The sheet resistance values for copper sulfide layers formed on the polyamide surface are much lower than those of Cu _x S formed on the polyethylene surface. XRD showed the predomination of Cu _x S phases with low x values.      

Formation and study of mixed copper sulfide-copper telluride layers on the surface of polyamide 6

The layers of mixed copper chalcogenides, Cu_xS-Cu_yTe, were formed on the surface of polyamide using solutions of potassium and sodium telluropentathionates, K₂TeS₄O₆ and Na₂TeS₄O₆, respectively, and of telluropentathionic acid, H₂TeS₄O₆, as precursors of chalcogens. The concentration of sorbed chalcogens increased with the increasing time of the treatment, concentration and temperature of precursor solution. Cu_xS-Cu_yTe layers are formed on the surface of polyamide after the treatment of chalcogenized polymer with Cu(II/I) salt solution. The concentration of copper in the layer increases with the increase of chalcogenization duration, concentration and the temperature of chalcogenization solution. In the surface of Cu_xS-Cu_yTe layers various copper, sulfur, tellurium and oxygen compounds (Cu₂S, CuS, S₈, Cu_xS, Cu_yTe, Cu(OH)₂ and TeO₂) were present. Chalcogenides were the major components in the layer. Chalcogenide phases — digenite, Cu_1.8S, djurleite, Cu_1.9375S, anilite, Cu₇S₄, geerite, CuS₂, chalcocite, Cu₂S, tetragonal Cu_3.18Te₂, Cu_2.72Te, hexagonal Cu₂Te, Cu₄Te₃, Cu_1.80Te, Cu_1.85Te₂, and orthorhombic vulcanite, CuTe were identified in the layers by X-ray diffraction. Electrical sheet resistance of Cu_xS-Cu_yTe layers vary from ∼ 1.0 kW cm⁻² to 4×10³ kΩ cm⁻². It is concluded that the formation of chalcogenide layers proceeds in the form of islands which grow into larger agglomerates. Use of the gathered data enables design and formation of the Cu_xS-Cu_yTe layers with desired conductivities.      

Comparison characterization of copper selenide thin layers prepared on polyamide 6 films by sorption-diffusion method

Some earlier synthesized copper selenide (Cu _x Se) layers formed on the surface of polyamide 6 by sorption-diffusion method using potassium selenotrithionate (K₂SeS₂O₆) as precursor of selenium were characterized by the XRD, XPS and SEM methods. According to the results of the SEM studies, the most uniform Cu _x Se layers form at the 2.5 h polyamide seleniumized duration at the temperature of 60°C. The thickness of layers, which dependeds on the duration of seleniumization, changed in the range of 0.8–3.2 µm. The XRD patterns of not previously studied Cu _x Se layers showed their phase composition of six copper selenides: Cu₂Se, two phases of CuSe₂, Cu₃Se₂, berzellianite, Cu_2-x Se, and bellidoite Cu₂Se. Analysis of the XRD and XPS data shows that the macrostructure and composition of the Cu_xSe layers depend on the conditions of formation of these layers.      

Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

The phase study of the TlVS system and the properties of TlV6S8 and TlV5S8 phases

The ternary phase diagram of the TlVS system was investigated using samples quenched from 400°C, especially in the neighborhood of TlV₆S₈ and TlV₅S₈ phases. The TlV₆S₈ phase (Tl_xV₆S_y) exists between 0.75 < x < 1.00 and 7.55 < y < 7.90, and the TlV₅S₈ phase (Tl_x′V₅S_y′) between 0.70 < x′ < 1.00 and 7.54 < y′ < 7.98. A new ternary phase with the nominal composition of TlV₂S₄ was found in addition to the three known ternary phases. The entirely deintercalated V₆S_7.8 with the framework structure was obtained by using 1 N AlCl₃ + 0.01 N FeCl₃ aqueous solution, while the lower phase limit of the TlV₅S₈ phase was Tl_0.33V₅S₈ consistent with the earlier work. The electrical resistivity and the magnetic susceptibility measurements show that these compounds are expected to be weakly magnetic itinerant-electron systems.     

Les thio-complexes du thallium en solution aqueuse

The solubility of thallium sulfide in 1M NaClO₄ at 25° ranges between 10⁵M as a function of pH and total sulfide concentration. Soluble thallium was analysed by anodic stripping using the hanging mercury drop electrode. The following complexes have been identified and their stability constants calculated: Tl₂(HS)⁺, Tl(HS), Tl₂(OH) (HS) and Tl₂(OH)₂(HS).     

Tuning the textural and surface properties of carbon xerogels to be used as supports for gold catalysts

Carbon xerogels (CXs) synthesized from resorcinol and formaldehyde under different pH conditions were investigated. Both the textural and surface properties of the CXs depend closely on the pH used in the synthesis procedure. Concerning the texture, the mesoporous surface area (S_meso) increases and the micropore volume (V_micro) decreases as the pH increases; concerning the surface chemistry, surface oxygen functional groups were easier to be created (by O₂) on CX synthesized at lower pH. Application of these CXs as support of gold catalysts was also studied. Results showed that the oxygen activated CX that was synthesized at moderate pH (i.e., pH 6.0) was the most favorable support for gold catalysts used in selective oxidation of benzyl alcohol by molecular oxygen in liquid phase, due to the adequate amounts of surface oxygen functional groups created on the surface.      

Surface degradation of fluoride conducting crystals MF2:UF4:CeF3 (M = Ca,Sr, Ba)

The ac electrical response of cell systems composed of single crystals of the concentrated solid solutions M_1?x?yU_xCe_yF_2+2x+y (M = Ca, Sr, Ba and 2.7 < 2x + y < 26.5 m/o), and ionically blocking electrodes has been studied as a function of frequency and temperature. At elevated temperatures the crystals react with traces of oxygen or water vapor. Complex admittance analysis reveals the formation of low-conducting surface layers, contrary to diluted solid solutions which under similar conditions react to form high-conducting surface layers (2). The activation enthalpy for the layer conductivity is substantially larger than that for the bulk conductivity, and equals that for interstitial fluoride ion motion in dilute solid solutions. A mechanism of charge compensation in the layers is presented. After reaction the solid solutions based on CaF₂ show also a surface electronic conductivity. Scanning electron micrographs clearly reveal the surface degradation.     

Normal pressure synthesis of (Tl1−yCy)Ba2Ca3Cu4O12−δ superconductor

Single phase (Tl_1−yC_y)Ba₂Ca₃Cu₄O_12−δ (Tl_1−yC_y-1234) (y = 0, 0.25, 0.5 and 0.75) superconductor samples have been prepared by solid state reaction method. The FTIR absorption measurements have confirmed the substitution of carbon at thallium site in the charge reservoir layer, (Tl_1−yC_y)Ba₂O_4−δ. The electron micrographs of these samples have shown that the carbon substitution has improved the grain morphology of Tl_0.75C_0.25-1234 sample. The y = 0.25 was found to be the optimum carbon concentration to achieve higher superconducting transition temperature T_c[0] and improved grain morphology. The superconducting transition temperature of Tl_0.75C_0.25-1234 sample has been increased to 100 K whereas a decrease in the superconducting transition temperature of Tl_1−yC_y-1234 (y = 0.5 and 0.75) samples was observed. However, the magnitude of diamagnetism has been decreased in all the carbon substituted samples.     

Anomalies in the properties of Hf(S2−xTex)1−y and Hf(Se2−xTex)1−y near the metal-insulator transition

The solid solutions Hf(S_2?xTe_x)_1?y and Hf(Se_2?xTe_x)_1?y were prepared to examine changes in the electronic structure in a narrow composition range near the metal-insulator transition. Powder X-ray diffraction analysis and resistivity measurements are presented. The x³ dependence of the hexagonal c parameter for the sulfur solutions is due to large packing mismatches in the layers. In the selenium solutions, anomalous behavior is observed in the composition dependence of the a and c hexagonal lattice parameters in the range 0.05 < x < 0.10, y ～ 0. Between these concentration limits, both lattice parameters show positive deviations from smooth behavior and the diffraction linewidths broaden. The temperature dependence of the resistivity suggests that the Hf(S_2?xTe_x)_1?y solutions have an energy of activation for conduction at room temperature for $\text{0 < x <}\text{7}\text{8}$; the sample of composition $\text{x =}\text{5}\text{8}$ has a metal-insulator transition as a function of temperature below room temperature. The band gap goes to zero with composition for Hf(Se_2?xTe_x)_1?y in the range x = 0.080 to x = 0.095. Nonstoichiometry, phase separation, and changes from covalent to metallic bonding explain the structural and electronic changes observed in the seleno-telluride system near the metal-insulator transition.     

Influence of temperature on the reduction kinetics of Bi(III) ion in the presence of cystine in chlorate (VII) solutions of decreased water activity

The results of the kinetic measurements of Bi(III) electroreduction on a mercury electrode in 1–8 mol dm^?3 chlorate (VII) solutions and in the presence of cystine demonstrate a dependence of the process on the temperature. The applied electrochemical techniques (DC polarography, cyclic and SWV voltammetry) allowed for the determination of the kinetic and thermodynamic parameters and their correlation with water activity. The catalytic activity of cystine was confirmed by the decrease in overall enthalpies of activation. The changes in the values of ΔH ^≠ and ΔS ⁰ for Bi(III) electroreduction in the presence of cystine with the increase of chlorate (VII) concentration showed that the mechanism is different in solutions with low water activity as compared to those with high water activity. Probably it is connected with a different structure of the activated complexes (Bi-Hg(SR)₂), mediating electron transfer.      

Theoretical investigations on thallium halides: Relativistic and electron correlation effects in T1X and T1X3 compounds (XF,C1, Br,and I)

Relativistic and electron correlation effects in thallium halides TlX and TlX₃ (X?F, Cl, Br, and I) are investigated by extensive ab initio configuration interaction calculations. Spin–orbit coupling is included at the Hartree–Fock level for the diatomic TlBr and TlI. At the best level of treatment of electron correlation (quadratic configuration interaction), the calculated molecular properties are in good agreement with experimental results, i.e., for the diatomic thallium halides deviations from experimental values are <0.06 Å for bond distances, <0.14 mdyn/Å for force constants, <35 kJ/mol for dissociation energies, and <0.3 D for dipole moments. The convergence of the Møller–Plesset series up to the fourth order is discussed. Two alternative structures of TlI₃ are compared. At the Møller–Plesset level of theory, the trigonal planar structure with thallium in the oxidation state + 3 is the preferred gas phase arrangement compared with the bent arrangement containing a linear I unit and thallium in the oxidation state + 1, the difference being ca. 95 kJ/mol. Vibrational frequencies are predicted for all trigonal planar thallium(III) halides. © 1993 John Wiley & Sons, Inc.     

Preparation and Mo¨ssbauer studies of (FeyNb1−y)1+xS2 compounds

The phase relations for iron niobium sulfides (Fe_yNb_1?y)_1+xS₂ have been examined by varying the partial pressure of sulfur at 950°C. While niobium is difficult to dissolve in iron sulfide, iron dissolves in niobium sulfide up to about 35% of the total metal sites. Iron niobium sulfide has the layered hexagonal type structure (2s-Nb_1+xS₂) with change in the lattice parameters depending on both the value of x and the amount of the iron dissolved. The Mo¨ssbauer spectra of sulfides with three different Fe/Nb ratios, 1/9(y =1/10), 1/4(y =1/5), and 1/2(y =1/3) were taken at 77 and 295 K. Each spectrum is composed of a quadrupole doublet which can be attributed to the Fe²⁺ ions in high spin state. The quadrupole splitting at 295 K decreases markedly with decrease in x which is related to change of the lattice parameters. Fe atoms cannot enter at random into all metal sites, and prefer to intercalate in the sites of partially filled layers. Possible models for the cation distribution in each metal layer are discussed.     

Obtaining nanostructured films of PbSe<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>S<Subscript>1–<Emphasis Type="Italic">y</Emphasis></Subscript> solid solutions by chemical deposition

We propose a technique for wet-chemical codeposition of lead sulfide and selenide using thiourea and selenourea to form films of PbSe _y S_1–y substitutional solid solutions. The synthesized nanocrystalline layers with NaCl (B1) structure simultaneously contain both PbS-based and PbSe-based PbSe _y S_1–y solid solutions (0 < y < 0.9).     

Nonenzymatic sensor for glucose based on a glassy carbon electrode modified with Ni(OH)2 nanoparticles grown on a film of molybdenum sulfide

A glassy carbon electrode (GCE) was modified with nickel(II) hydroxide nanoparticles and a film of molybdenum sulfide. The nanocomposite was prepared by two-step electrodeposition. Scanning electron microscopy reveals that the nanoparticles are uniformly deposited on the film. Cyclic voltammetry and chronoamperometry indicate that this modified GCE displays a remarkable electrocatalytic activity towards nonenzymatic oxidation of glucose. Response is linear in the 10–1,300 μM concentration range (R ² ?=?0.9987), the detection limit is very low (5.8 μM), response is rapid (< 2 s), and selectivity over ascorbic acid, dopamine, uric acid, fructose and galactose is very good.

Electromediators based on the Ni(II) and Cr(III) complexes with the redox-active ligands in the synthesis of sulfur-containing organic compounds

The chromium(III) tris-o-semiquinolate complex Cr(L^SQ)₃ (L^SQ is 3,6-di-tert-butyl-o-semiquinone) and the monoanionic paramagnetic nickel(II) complex [n-Bu₄N][Ni(L _S ^SQ )(L _S ^DT )] (L _S ^SQ is o-thiosemiquinone, L _S ^DT is benzene-1,2-dithiolate) are considered as electromediators of hydrogen sulfide oxidation in the presence of various organic substrates (hex-1-ene, oct-1-ene, benzene, toluene, and benzoic acid). It is revealed that the electrolysis of hydrogen sulfide at the oxidation potential of the mediators in the presence of the substrates affords the corresponding aliphatic and aromatic thiols in a yield of 62–75%.     

Les systèmes MFTlF3 (M = Li,Na, K)

A large number of new phases have been prepared and characterized in the MFTlF₃ system: Na₃TlF₆ isostructural with cryolite, Na₃Tl₂F₉, Na_xTl_1−xF_3−2x (0.425 ? x ? 0.565 at 500°C) and Na₅Tl₉F₃₂ related to the fluorite type, K₃TlF₆ with a structure similar to that of (NH₄)₃FeF₆, K₅Tl₃F₁₄ with the chiolite structure, Na_yTl_1−yF_3−2y (0.12 ? y ? 0.14 at 500°C) and K₂Tl₇F₂₃ affiliated to α-UO₃, KTlF₄, and KTl₂F₇.     

Copper-cobalt ferrites as catalysts for methanol decomposition

Copper-cobalt ferrites with composition Cu_1?xCo_xFe₂O₄, where x= 0.2 and 0.8 were prepared by thermal treatment of co-precipitated precursor. The obtained materials were characterized by TG-DSC, XRD, Transmission and Conversion Electron Mössbauer spectroscopy and temperature programmed reduction with hydrogen. The catalytic properties of ferrites were tested in methanol decomposition to CO and hydrogen.      

The clathrate Ba8CuxGe46−x−y□y: Phase equilibria and crystal structure

Phase relations at 700 °C, 800 °C and solidus temperatures have been derived for the clathrate system Ba₈Cu_xGe_46−x−y□_y via X-ray single crystal and powder diffractometry combined with electron probe micro analysis and differential thermal analysis. The ternary clathrate phase derives from binary Ba₈Ge₄₃□₃ and extends up to x=6. Structure investigations define cubic primitive symmetry with the space group type consistent with a clathrate type I structure throughout the entire homogeneity region 0<x?6 but defect-free Ba₈Cu_xGe_46−x exists for x?5.5.