Oxygen potential, oxygen diffusion, and defect equilibria in UO2±x

The oxygen nonstoichiometry x and the chemical diffusion coefficient of oxygen in Ba2YCu3O7−x were measured by means of thermogravimetry as a function of oxygen partial pressure and temperature over the ranges 102 <Po2/Pa<105and 698<T/K<1173. The oxygen partial pressure dependence of x in Ba2Cu3O7−x obtained in this study was in good agreement with those previously reported by other researchers. The chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various oxygen nonstoichiometry x=0.063–0.77 were measured, and they increased with decreasing oxygen nonstoichiometry x at constant temperature. The compositional dependence of the chemical diffusion coefficient changed at about x=0.35, indicating the occurrence of the phase transition from the tetragonal to the orthorhombic structure. The activation energies of the chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various x were observed to be about 115·kJ mol−1, irrespective of oxygen nonstochiometry x. The self-diffusion coefficient of oxygen and the diffusion coefficient of oxygen vacancy were calculated from the chemical diffusion coefficient, and were compared with those of another superconductor La2−ySryCuO4−x.

Crystal structure, oxygen nonstoichiometry, and mass and charge transport properties of the Sr-free SOFC/SOEC air electrode material La0.75Ca0.25FeO3-δ

Chemical diffusion coefficient of oxygen in thoria based fuel with 3 and 8 weight % urania

The solid state electrochemical technique is a convenient method for assessment of the chemical diffusion coefficient of oxygen in electronically conducting perovskites. The interpretation is usually based on a number of assumptions, of which one of the most important is one-dimensional diffusion. In this work the authors describe potential step measurements on sealed samples of SrCo{sub 1{minus}x}Fe{sub x}O{sub 3{minus}{delta}}, focusing per se on the assumptions underlying the technique and the interpretation of results. A lack of sample-thickness dependence of the measured time constants is thus taken to indicate the presence of high-diffusivity paths in the specimens, possibly owing to open porosity. This indicates that a high pellet density may be required for a proper assessment of diffusion coefficients.

Diffusion properties of oxygen in the α2-Ti3Al alloy

Oxygen potentials of uranium-plutonium oxides in the near stoichiometric region

In this work, fundamental material properties of compounds in the system (La,Pr)2(Ni,Co)O4+δ as well as their performance as air electrodes in solid oxide electrolysis cells were investigated. Nickelates co‐doped with Pr and Co were characterized on a material basis by means of X‐ray diffraction and thermogravimetry. Conductivity and conductivity relaxation measurements were performed in order to obtain the electronic conductivity as well as the chemical surface exchange coefficient and the chemical diffusion coefficient of oxygen as a function of temperature and oxygen partial pressure. These parameters can be regarded as the most essential properties at the material level required to assess the suitability of mixed ionic‐electronic conducting ceramics for application as air electrode in solid oxide cells. The electrode performance of the materials was then tested on fuel electrode‐supported button cells at 800°C. The electrodes were applied by screen‐printing and the effect of varying the Pr‐content and Co‐content of the electrode powder was investigated. Cell tests were performed by means of current‐voltage measurements in electrolysis mode. While no significant impact of Pr‐doping on the investigated material properties was observed, the electrode performance of Pr‐containing materials was significantly better than for the Pr‐free compound, which has been discussed in detail.

The diffusion of oxygen in the cornea

Sodium ion batteries have been receiving increasing attention and may see potential revival in the near future, particularly in large-scale grid energy storage coupling with wind and solar power generation, due to the abundant sodium resources, low cost, and sufficiently high energy density. Among the known sodium ion conductors, the Na-β”-alumina electrolyte remains highly attractive because of its high ionic conductivity. This study focuses on the vapor phase synthesis of a Na-β”-Alumina + YSZ (Naβ”AY) composite sodium electrolyte, which has higher mechanical strength and stability than conventional single phase β”-Alumina. The objectives are the measurement of conversion kinetics through a newly developed weight-gain based model and the determination of sodium ionic conductivity in the composite electrolyte. Starting samples contained ~70 vol% α-Alumina and ~30 vol% YSZ (3 mol% Y2O3 stabilized Zirconia) with and without a thin alumina surface layer made by sintering in air at 1600 °C. The sintered samples were placed in a powder of Na-β”-alumina and heat-treated at 1250 °C for various periods. Sample dimensions and weight were measured as a function of heat treatment time. The conversion of α-Alumina in the α-Alumina + YSZ composite into Naβ”AY occurred by coupled diffusion of sodium ions through Na-β”-alumina and of oxygen ions through YSZ, effectively diffusing Na2O. From the analysis of the time dependence of sample mass and dimensions, the effective diffusion coefficient of Na2O through the sample, , was estimated to be 1.74 × 10−7 cm2 s−1, and the effective interface transfer parameter, , was estimated as 2.33 × 10−6 cm s−1. By depositing a thin alumina coating layer on top of the bulk composite, the chemical diffusion coefficient of oxygen through single phase Na-β”-alumina was estimated as 4.35 × 10−10 cm2 s−1. An AC impedance measurement was performed on a fully converted Naβ”AY composite, and the conductivity of the composite electrolyte was 1.3 × 10−1 S cm−1 at 300 °C and 1.6 × 10−3 S cm−1 at 25 °C, indicating promising applications in solid state or molten salt batteries at low to intermediate temperatures.

Strontium-free rare earth perovskite ferrites with fast oxygen exchange kinetics: Experiment and theory

A new class of oxygen selective chemically driven nonporous ceramic membranes. Part I. A-site doped perovskites

Mesures de resistivite et de cinetique d'oxydation dans PuO 2− x

Layered oxides of Sr4Fe4Co2O13 (SFC2) which contains alternating perovskite oxide octahedral and polyhedral oxide double layers are attractive for their mixed ionic and electronic conducting and oxygen reduction reaction properties. In this work, we used the EDTA–citrate synthesis technique to prepare SFC2 and vary the calcination temperature between 900 and 1100 °C to obtain SFC2, containing different phase content of perovskite (denoted as SFC-P) and (Fe,Co) layered oxide phases (SFC-L). Rietveld refinements show that the SFC-P phase content increased from ∼39 wt% to ∼50 wt% and ∼61 wt% as the calcination temperature increased from 900 °C (SFC2-900) to 1000 °C (SFC2-1000) and 1050 °C (SFC2-1050). At 1100 °C (SFC2-1100), SFC-P became the dominant phase. The oxygen transport properties (e.g. oxygen chemical diffusion coefficient and oxygen permeability), electrical conductivity and oxygen reduction reaction activity is enhanced in the order of SFC2-1000, SFC2-1100 and SFC2-1050. The trend established here therefore negates the hypothesis that the perovskite phase content correlates with the oxygen transport property enhancement. The results suggest instead that there is an optimum composition value (e.g. 61 wt% of SFC-L for SFC2-1050 in this work) on which synergistic effects take place between the SFC-P and SFC-L phase.

NiAl2O4 spinel was formed by solid state reaction. Its electrical conductivity was measured in the temperature range of 680–940 °C and under various oxygen-rich environments, as well as under reducing conditions. From the temperature dependence of the conductivity, the activation energies for conduction increase for decreasing oxygen partial pressures. From the partial oxygen pressure dependence, the defect structure of the material was analysed. The conductivity change with respect to PO2 can be attributed to singly and doubly ionized nickel vacancies. The chemical diffusivity of the oxide was determined by conductivity relaxation upon abrupt change in PO2 in the surrounding atmosphere. The oxygen chemical diffusion coefficient is of the order of magnitude of 10−4 cm2 s−1.

Doping effects of alkaline earth element on oxygen reduction property of high-entropy perovskite cathode for solid oxide fuel cells