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.     

Interaction of Cl<Subscript>2</Subscript> and SO<Subscript>2</Subscript> with Finely Divided In<Subscript>2</Subscript>O<Subscript>3</Subscript>

The effect of O₂, Cl₂, and SO₂ on electrophysical and sorption properties of powdered In₂O₃ with a large specific area is studied at 23–200°C. The specimen is most sensitive to Cl₂ and SO₂ at near-room temperatures.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 529–536.Original Russian Text Copyright © 2005 by Vinokurova, Derlyukova.     

Endohedral Complex of Fullerene C<Subscript>60</Subscript> with Tetrahedral N<Subscript>4</Subscript>, N<Subscript>4</Subscript>@C<Subscript>60</Subscript>

B3LYP/6-31G(d) hybrid HF/DFT and BLYP/6-31G(d, p) DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C₆₀ with Tetrahedral N₄ (T_d N₄), N₄@C₆₀. It was demonstrated that N₄ was seated in the center of the fullerene cage and the tetrahedral structure of N₄ is remained in the cage. The formation of this complex is endothermic with inclusion energy of 37.92 kcal/mol. N₄ endohedral doping perturbs the molecular orbitals of C₆₀ not so much, the calculated HOMO–LUMO gaps, the electron affinity (EA) and the ionizational potential (IP) of N₄@C₆₀ are similar to that of C₆₀.     

Solid electrolytes with cesium-cationic conduction in the Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Cs<Subscript>2</Subscript>O system

New cesium-conducting solid electrolytes based on cesium monoferrite in the Fe₂O₃-TiO₂-Cs₂O system are synthesized and studied. It is found that the introduction of titanium dioxide significantly reduces the electronic component of conductivity, which prevails in pure CsFeO₂, and raises the ionic conductivity. The latter becomes predominant with increasing concentration of TiO₂. The effect of dimensional factor on the characteristics of electrolyte is shown. The optimal compositions studied have very high cesium-cationic conductivity: it is above 10⁻² S cm ⁻¹ at 300°C.     

Electochemical characteristics of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> battery with conducting polymeric binder

Lithium-ion battery based on LiMn₂O₄/Li₄Ti₅O₁₂ materials was assembled for the first time. The cathode and anode of this battery are prepared with the aqueous combined binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose (without polyvinylidene fluoride). The capacity of the LiMn₂O₄/Li₄Ti₅O₁₂ battery was found to be 75 mA h g^–1 at 0.1 C and 55 mA h g^–1 at 1 C. A 95% capacity was retained after 100 charge-discharge cycles. The batteries demonstrated a high Coulombic efficiency close to 100%. Scanning electron microscopy demonstrated that using the conducting binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose provides formation of dense compact layers of electrode materials with good adhesion to the substrate. The electrode structure remains maintained after 100 charge-discharge cycles.     

Stabilization of Oil-in-Water Emulsions with SiO<Subscript>2</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

Stabilization of oil-in-water Pickering emulsions with SiO₂ and Fe₃O₄ nanoparticles has been studied. Emulsions containing three-dimensional gel networks formed by aggregated nanoparticles in the dispersion media have been shown to be stable with respect to flocculation, coalescence, and creaming. Concentration ranges in which emulsions are kinetically stable have been determined. Stabilization with mixed Ludox HS-30 and Ludox CL SiO₂ nanoparticles leads to the formation of stable emulsions at a weight ratio between the nanoparticles equal to 2 and pH 6.7. In the case of stabilization with Ludox CL and Fe₃O₄ nanoparticles, systems resistant to aggregation and sedimentation are obtained at pH 8. The use of mixed Ludox HS-30 and Fe₃O₄ nanoparticles has not resulted in the formation of emulsions stable with respect to creaming, with such emulsions appearing to be resistant only to coalescence at pH 2–6.     

Study of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> interaction with solid lithium-containing electrolytes

Compatibility of the lithium-titanium spinel Li₄Ti₅O₁₂ in contact with precursors of lithium-conducting solid electrolytes of composition Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), Li_0.5La_0.5TiO₃ (LLT) was studied. It was found that, in sintering of Li₄Ti₅O₁₂ brought in contact with LATP and LAGP, a solid-phase reaction occurs to give nonconducting phases (TiO₂ and Li₃PO₄). The conductivity of the stable composite Li₄Ti₅O₁₂/LLT (10%) is higher than that of the starting Li₄Ti₅O₁₂, which makes it possible to regard the composite as a promising anode material for lithium-ion batteries.     

New metal-rich mixed chalcogenides with an intergrowth structure: Ni<Subscript>5.68</Subscript>SiSe<Subscript>2</Subscript>, Ni<Subscript>5.46</Subscript>GeSe<Subscript>2</Subscript>, and Ni<Subscript>5.42</Subscript>GeTe<Subscript>2</Subscript>

New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni_5.68SiSe₂, Ni_5.46GeSe₂, and Ni_5.42GeTe₂, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M_7−δEX₂-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the intergrowth structure type under consideration are discussed. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007.     

CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>-Based materials with variable copper content

The CaO-3 (1 + x)CuO-4TiO₂ system was studied using powder X-ray diffraction in the concentration region near calcium copper titanate. A single-phase material is formed in this system only when x ～ 0. An excess or deficit of copper gives rise to extra phases: CuO or CaTiO₃ and TiO₂, respectively. Impurities increase the dielectric constant of CaCu₃Ti₄O₁₂-based ceramics. An excess of copper oxide (x ～ 0.08) increases ? more than tenfold.     

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.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.     

Interaction of solid electrolyte La<Subscript>0.88</Subscript>Sr<Subscript>0.12</Subscript>Ga<Subscript>0.82</Subscript>Mg<Subscript>0.18</Subscript>O<Subscript>2.85</Subscript> with hydrogen,water vapor,and carbon dioxide

The air,Au/La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85/Au,air cells are studied by an impedancemetry method before and after a week-long exposure at 700°C to atmospheres of hydrogen, humid air, and carbon dioxide. Blank specimens of the same electrolyte are examined by methods of x-ray diffraction, Raman scattering (RS), and x-ray photoelectron spectroscopy. The fact that the shape of the RS spectra and the shape of the electrode impedance dispersion alter unequivocally suggests that, at the very least, the electrode surface interacts with all the gases. The interaction in question is reversible in the case of hydrogen and carbon dioxide. In the case of water vapor, the interaction is irreversible.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 198–205.Original Russian Text Copyright © 2005 by Shkerin, Kovyazina, Beresnev, Kalashnikova, Martemyanova.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Solid electrolytes with cesium cation conductivity in the Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Cs<Subscript>2</Subscript>O system

Solid solutions based on cesium monogallate CsGaO₂ are synthesized in the Ga₂O₃-TiO₂-Cs₂O system. Their crystalline structure and also temperature and concentration conductivity dependences are studied. The cesium cation character of conductivity is confirmed. The most conducting samples contain an excess of cesium oxide and have the structure of high-temperature γ-modification of KAlO₂. Their specific conductivity is (5.0–6.7) × 10^?3 S cm^?1 at 400 °C, (2.5–5.0) × 10^?2 S cm^?1 at 700°C at the activation energy of 33–35 kJ/mol^?1.     

Isothermal crystallization kinetics of Fe<Subscript>75</Subscript>Cr<Subscript>5</Subscript>P<Subscript>9</Subscript>B<Subscript>4</Subscript>C<Subscript>7</Subscript> metallic glass with cost-effectiveness and desirable merits

In this work, the isothermal crystallization kinetics of cost-effective Fe₇₅Cr₅P₉B₄C₇ metallic glass with a combination of desired merits synthesized by industrial ferro-alloys without high-purity materials was evaluated by Johnson–Mehl–Avrami approach using differential scanning calorimeter. The Avrami exponents at all isothermal annealing temperatures range from about 2.93 to 4.61, indicating a three-dimensional diffusion-controlled growth with an increasing nucleation rate during the isothermal crystallization. Meanwhile, the Avrami exponent firstly increases from 2.93 at the initial time to a maximum value of 4.61 and then decreases to 4.09 with the increment of the isothermal annealing temperature, which can be attributed to the atomic diffusion in the alloy. Additionally, the trend of the local Avrami exponent variations at different isothermal annealing temperatures reflects a variable crystallization mechanism during the crystallization process. Moreover, the local activation energy determined by Arrhenius equation gradually decreases from about 412 to 383 kJ mol^?1 during the present isothermal crystallization, further revealing that the process is dominated by a three-dimensional diffusion-controlled growth with an increasing nucleation rate, which provides useful insights into the formation of the present alloy.     

Lithium AlPO<Subscript>4</Subscript> composite polymer battery with nanostructured LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode

The borate ester plasticized AlPO₄ composite solid polymer electrolytes (SPE) have been synthesized and studied as candidates for lithium polymer battery (LPB) application. The electrochemical and thermal properties of SPE were shown to be suitable for practical LPB. Nanostructured LiMn₂O₄ with spherical particles was synthesized via ultrasonic spray pyrolysis technique and has shown a superior performance to the one prepared via conventional methods as cathode for LPB. Furthermore, the AlPO₄ addition to the polymer electrolyte has improved the polymer battery performance. Based on the AC impedance spectroscopy data, the performance improvement was suggested as being due to the cathode/polymer electrolyte interface stabilization in the presence of AlPO₄. The Li/composite polymer electrolyte/nanostructured LiMn₂O₄ electrochemical cell showed stable cyclability during the various current density tests, and its performance was found to be quite acceptable for practical utilities at ambient temperature and showed remarkable improvements at 60 °C compared with the solid state reaction counterpart.     

Three-component systems LiBr-LiVO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript> and LiBr-Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>-Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>

Phase equilibria in the three-component systems LiBr-LiVO₃-Li₂MoO₄ and LiBr-Li₂SO₄-Li₂MoO₄ have been studied using differential thermal analysis (DTA). Eutectic compositions have been determined (mol %): in the system LiBr-LiVO₃-Li₂MoO₄, 56.0 LiBr, 22.0 LiVO₃, and 22.0 Li₂MoO₄ with a melting temperature of 413°C; and in the system LiBr-Li₂SO₄-Li₂MoO₄, 65.0 LiBr, 14.0 Li₂SO₄, and 21.0 Li₂MoO₄ with a melting temperature of 421°C. Phase fields have been demarcated.     

Promoted photoelectrochemical activity of BiVO<Subscript>4</Subscript> coupled with LaFeO<Subscript>3</Subscript> and LaCoO<Subscript>3</Subscript>

BiVO₄ has emerged as a promising material for solar water splitting. The poor ability of charge transport and separation always limits its performance for photoelectrochemical water splitting. Herein, we coupled n-type BiVO₄ with p-type LaFeO₃ and LaCoO₃, achieving a photocurrent more than two times as high as bare BiVO₄ at 1.23 V versus a reversible hydrogen electrode. Also, the onset potential was negatively shifted about 260 mV. The promotion of performance is mainly because the space charge layer in BiVO₄ is broadened, and the band bend is enhanced, which facilitates the separation and transport of photo-generated charges.     

Cyclopropanation of alkynols with the CH<Subscript>2</Subscript>I<Subscript>2</Subscript>-R<Subscript>3</Subscript>Al system

Acetylenic alcohols bearing two or three methylene groups between the triple bond and hydroxy group react with CH₂I₂ in the presence of trialkylalanes to give 1,1,2-tri- and 1,1,2,2-tetrasubstituted cyclopropanes.     

Compatibility of TiO<Subscript>2</Subscript> with a CaO-CaCl<Subscript>2</Subscript> melt

Interaction of TiO₂ with a CaO-CaCl₂ melt was studied to determine whether electrolytic production of titanium from oxide raw materials is possible.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.