The diffusion of oxygen and ion transport in lanthanum cobaltite LaCoO<Subscript>3-δ</Subscript>

The chemical diffusion coefficient of oxygen vacancies and oxygen ion conductivity in lanthanum cobaltite LaCoO₃ were determined by the polarization method as functions of oxygen partial pressure \(p_{O_2 } \) (atm) and temperature T(K) over the ranges ?4 ≤ log \(p_{O_2 } \) ≤ 0 and 1173 K ≤ T ≤ 1323 K. The mobilities (cm²/(V s)) of oxygen vacancies calculated over the temperature range studied satisfy the inequalities 1.8 × 10^?5 ≤ \(v_{v_0 } \) ≤ 3.4 × 10^?5. The transfer numbers of oxygen vacancies were calculated. These numbers change depending on oxygen partial pressure over the range 5 × 10^?7 ≤ t ₀ ≤ 1 × 10^?5. The activation energy of self-diffusion of oxygen vacancies was found to be E _a= 104 ± 10 kJ/mol (1.1 ± 0.1 eV).     

Equilibrium of point defects and charge transfer in lanthanum cobaltite

The specific conductivity logσ _T and thermal electromotive force coefficient Q _T of perovskite-like lanthanum cobaltite were measured over the temperature range 1173 K ≤ T ≤ 1323 K depending on the partial pressure of oxygen (10⁻⁸ atm ≤ p _{O 2} ≤ 1 atm). The p _{O 2}-T-δ phase diagram of solid LaCoO_3-δ studied earlier was used to recalculate the electric property data into the log σ _T -δ and Q _T -δ dependences. The isoconcentration temperature dependences of specific conductivity (logσ)_δ-1/T and Seebeck coefficient Q _δ-1/T for LaCoO_3-δ were analyzed. The conclusion was drawn that charge transfer was activation in character and had a low activation energy. This was evidence that small-radius polarons (Co ^•_Co and Co ^′_Co ) were responsible for charge transfer in perovskite-like lanthanum cobaltite. The calculated equilibrium constants for the formation of electronic defects and functional dependences of defect concentration [Co ^•_Co ] _T = f ₁(δ) and [Co ^′_Co ] _T = f ₂(δ) were used to analyze polaron transfer parameters in LaCoO_3-δ.

     

Formation and Properties of a Support Made of Solid Solutions Based on Zirconium Oxide for Single Tubular Solid-Oxide Fuel Cells

Technique was developed for fabrication of a supporting thin-walled gas-tight ZrO₂–Y₂O₃ electrolyte base of strict configuration for tubular solid-oxide fuel cells. The technique includes a plasma-assisted deposition and vacuum impregnation with salt solutions, followed by a thermal treatment. The properties of plasma-ceramic solid electrolytes based on cubic and tetragonal (t') forms of ZrO₂ and the same electrolytes modified with small additions (0.5 wt %) of aluminum oxide were examined. The phase composition, electrical conductivity, thermal expansion, and stability of the materials synthesized were studied. A high stability in time of the tetragonal t'-solid electrolytes was noted, which opens up prospects for their application in solid-oxide fuel cells.     

Study of nanostructured catalysts on the basis of complex oxides deposited on a carrier

A catalyst on the basis of complex oxide with perovskite structure deposited on a cellular nickel has been studied by scanning and transmission electron microscopy. The presence of the porous structure of the catalytic coating and its nature and the particle size of the catalytic phase have been established. The morphology of the intermediate layers has been studied. Such intermediate layers appearing in the case in which a secondary carrier (aluminum oxide) is used have a promoting effect on the catalyst. The regularities of the formation of ensembles of particles of the perovskite phase depending on the conditions of synthesis by pyrolysis of polymer salt compositions, such as the nature of the organic component, the ratio between the oxidant and the reductant, thermal treatment temperature have been studied.     

Paramagnetic copper centers in ferroelectric lead germanate with halogens

The electron paramagnetic resonance spectrum of triclinic bivalent copper centers in copper-doped Pb₅Ge₃O₁₁ single crystals has been investigated. The spectrum intensity increases after thermal treatment in a chlorine- or fluorine-containing atmosphere. The parameters of the electron Zeeman, hyperfine, and nuclear quadrupole interactions have been determined. The model of the observed centers has been proposed.     

Doped (Nd,Ba)FeO3 oxides as potential electrodes for symmetrically designed protonic ceramic electrochemical cells

Journal of Solid State Electrochemistry - The design of new electrode materials with high redox stability has great potential for the fabrication of solid oxide fuel and electrolysis cells having a...     

The oxygen nonstoichiometry and defect structure of unsubstituted LaCoO<Subscript>3−δ</Subscript> cobaltite

The paper presents the results obtained in studying the oxygen nonstoichiometry of undoped lanthanum cobaltite LaCoO_3?δ as a function of temperature and oxygen pressure. A model analysis of the defect structure of the compound was performed. Two models were considered. For the first model, it was assumed that electrons and electron holes were quasi-free, whereas, in the second model, they were considered localized on cobalt ions. The internal electronic disordering and thermally excited disproportionation of cobalt were also taken into consideration in the first and second models, respectively. For both models, systems of nonlinear equations comprising the corresponding mass action law, mass balance, and electroneutrality equations were constructed. Verification equations were obtained for both models by solving these systems. The correspondence of the suggested models to experimental data was checked by the nonlinear regression method. Both models almost equally correctly described the data on the oxygen nonstoichiometry of LaCoO_3?δ. The conclusion was drawn that these data were insufficient for selecting the most realistic model of the defect structure of this compound.     

Transport properties of iron-doped BaZr0.9Yb0.1O3–δ

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Assessment of prospective cathodes based on (1-x)Ca3Co4O9+δ-xBaCe0.5Zr0.3Y0.1Yb0.1O3-δ composites for protonic ceramic electrochemical cells

Journal of Solid State Electrochemistry - This work presents investigation of novel composite electrodes comprising misfit layered oxide Ca3Co4O9+δ and protonic conductor...     

The Formation of Dimeric Centers of Copper,Iron and Gadolinium in Modified Pb<Subscript>5</Subscript>Ge<Subscript>3</Subscript>O<Subscript>11</Subscript>

It is discovered that the electron paramagnetic resonance (EPR) spectrum of the doubly charged copper centers occurs in single crystals of Pb₅Ge₃O₁₁ doped with gadolinium or iron after annealing in an atmosphere containing chlorine and bromine. Similar annealing of the crystals doped with copper in a chlorine and fluorine atmosphere leads to redistribution of the intensities of the EPR spectra of two types of Cu²⁺ centers. The influence of annealing on the ongoing intensity of spectra of the dimeric triclinic centers Fe³⁺–A, Gd³⁺–A (where A represent Cl^?, Br^?, O^2?, F^?) was the subject of this research. Consideration is given to the mechanisms for changing the charge state and association of copper center with defects.