The electrochemical behavior of the LaSrCuO<Subscript>4 − δ</Subscript>/Ce<Subscript>0.9</Subscript>Gd<Subscript>0.1</Subscript>O<Subscript>2 − δ</Subscript> interface

The electrochemical behavior of the LaSrCuO_{4 − δ}/Ce_0.9Gd_0.1O_{2 − δ} interface is studied by impedance spectroscopy and cyclic voltammetry methods. By analyzing the dependence of the impedance frequency spectra on the oxygen partial pressure, the rate-determining stages of oxygen exchange are determined in the temperature interval of 500–900°C. For temperatures above 700°C, the adsorption of oxygen molecules and their dissociation to oxygen atoms are shown to make a substantial contribution to the polarization resistance of the overall electrode process, besides the charge-transfer resistance.     

Electrochemical Properties of Electrode Materials Based on Pr5Mo3O16 + δ

Russian Journal of Electrochemistry - The electrochemical activity of electrode materials based on Pr5Mo3O16 + δ (РМО), and applied on the surface of Ce0.9Gd0.1O1.95 (GDC)...     

Synthesis and photophysical properties of soluble polyimides and polyquinazolones containing side-chain chalcones or azo chromophores

Soluble aromatic and carboxyl- and hydroxyl-containing polyimides, mixed polyimides, and polyquinazolones of various chemical structures, as well as a series of new dicyanoazobenzene chromophores, are synthesized. From 20 to 80 mol % of chromophore groups are incorporated into side chains of the polymers. The thermal, photosensitive, and nonlinear optical properties (second-harmonic generation) of the chromophore-containing polymers are investigated. The polymers with covalently attached groups of the dye DR-13 or azo-derivatives of 4-phthalonitrile demonstrate the highest nonlinearity. The T _g values of the polyimides vary from 165 to 215°C; their temperatures corresponding to 5% weight loss lie in the range 290–350°C; and the measured coefficients of second-harmonic generation, d ₃₃, for a number of polarized films based on chromophore-containing polymers attain several tens of picometers per volt. The incorporation of chromophore groups into the side chains of the polymers causes an increase in the photosensitivity of polyimides by an order of magnitude relative to that of the parent polymers (S _0.1 = (3?4) × 10⁵ cm²/J in the range of dye absorption).     

Stabilized Zirconia-Based Nanostructured Powders for Solid-Oxide Fuel Cells

High-purity uniform powders of zirconia-based solid electrolytes stabilized with yttria (4 and 8 mol %) are synthesized by co-precipitation with subsequent annealing at different temperatures. The obtained powders were studied using X-ray analysis and transmission electron microscopy; the specific surface area was measured by nitrogen adsorption. The stabilized zirconia powder sintering was studied over temperature range from 1000 to 1600°C. The ionic conductivity of samples containing 8 mol % of yttria was 0.06–0.07 S/сm, that is comparable with that obtained with commercial solid electrolytes.     

Electrotransport properties of SOFC cathode materials based on lanthanum cuprate doped with praseodymium and strontium oxides

A complex study of thermal, conducting, and electrocatalytic properties of cuprates La_1.8?xPr_xSr_0.2CuO_4–δ (х = 0.2; 0.4) with the K₂NiF₄ structure is carried out in order to assess their prospects as the cathode materials for solid-oxide fuel cells. The thermal analysis reveals stability of samples heated up to 950°С in air. The conductivity of cuprates measured in the temperature range of 100–900°С and the partial oxygen pressure from 10^–3 to 1 atm is of the metallic nature and varies from 70 to 40 S/cm in the temperature interval of 500–900°С in air. The studies of chemical stability of cuprates with respect to solid electrolytes demonstrate the absence of their chemical interaction with Ce_0.9Gd_0.1O_1.95 (GDC) at 900°С and with La_0.8Sr_0.2Ga_0.85Mg_0.15O_3–δ (LSGM) at 1000°C after 25 h annealing. For La_1.6Pr_0.2Sr_0.2CuO_4–δ electrodes deposited on the surface of GDC or LSGM solid electrolytes, the studies of electrocatalytic activity in the oxygen reduction reaction demonstrate that the smallest polarization resistance is typical of electrodes deposited on the GDC surface.     

Physicochemical properties and mixed electronic and ionic conduction of composite ceramics in the system ZrO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

Composites ZrO₂-(Bi₂CuO₄+ 20 wt % Bi₂O₃) (50–80 vol % ZrO₂) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO₂ of a monoclinic modification, Bi₂CuO₄, and solid solution Bi_2?x Zr _x O_{3 + x/2} and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 10⁴ Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ～0.01 S cm^?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO₂ and 50 vol % (Bi₂CuO₄ + 20 wt % Bi₂CuO₄) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10^?8 mol cm^?2 s^?1, testifying that these materials may be used as gas-separating membranes.     

The synthesis and transport properties of the cuprates La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1 + <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>2</Subscript>O<Subscript>6 + δ</Subscript>

The cuprates La_{2 ? x} Sr_{1 + x} Cu₂O_{6 + δ}(x = 0, 0.1, 0.2) are synthesized by solid-state method. Their dc conductivity was studied over the 373 to 1173 K temperature range and 10 to 2.1 × 10⁴ Pa oxygen partial pressure range by using four-probe technique. It is shown that the cuprate conductivity in air is maximal at ～673 K; it is 60 S/cm for La₂SrCu₂O_6.09; 68 S/cm, for La_1.9Sr_1.1Cu₂O_6.18; and 81 S/cm, for La_1.8Sr_1.2Cu₂O_6.10. The thermal expansion coefficient of La₂SrCu₂O_6.09 is determined by thermomechanical method and high-temperature X-ray diffraction method; its value (16 ppm K^?1) shows that the material is compatible with the ceria-based solid electrolytes during the thermal cycling.     

Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides

Novel complex oxides Sr₂Ga_1+x In_1?x O₅, x?=?0.0–0.2 with brownmillerite-type structure were prepared in air at T?=?1,273 K, 24 h. Study of the crystal structure of Sr₂Ga_1.1In_0.9O₅ refined using X-ray powder diffraction data (S.G. Icmm, a?=?5.9694(1) Å, b?=?15.2091(3) Å, c?=?5.7122(1) Å, χ ²?=?2.48, R _F ²? ₌?0.0504, R _p?=?0.0458) revealed ordering of Ga³⁺ and In³⁺ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr²⁺ by La³⁺ according to formula Sr_1?y La _y Ga_0.5In_0.5O_2.5+y/2, leads to the formation of a cubic perovskite (a?=?4.0291(5) Å) for y?=?0.3. No ordering of oxygen vacancies or cations was observed in Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 as revealed by electron diffraction study. The trace diffusion coefficient (D _T) of oxygen for cubic perovskite Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 is in the range 2.0?×?10^?9–6.3?×?10^?8 cm²/s with activation energy 1.4(1)?eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973–1,223 K. These values are close to those reported for Ca-doped ZrO₂. High-temperature electrical conductivity of Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T?<?1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.     

High-temperature properties of new perovskite-like oxides

New complex oxides of composition Pr_1–y Ca _y Fe_{0.5 + x} (Mg_0.25Mo_0.25)_0.5–x O₃, 0.0 ≤ x ≤ 0.1, 0.42 ≤ y ≤ 0.8 having an orthorhombically distorted perovskite structure have been prepared. The thermal expansion and electric conductivity of the new phases have been studied in the temperature range between 100–900°C. The results of our study imply that thin films of the oxides studied can be treated as electrode materials for symmetric solid-oxide fuel cells.