Anisotropic Oxygen Ion Diffusion in Layered PrBaCo₂O_5+δ

Abstract

Oxygen diffusion and surface exchange coefficients have been measured on polycrystalline samples of the double perovskite oxide PrBaCo2O5+δ by the isotope exchange depth profile method, using a time-of-flight SIMS instrument. The measured diffusion coefficients show an activation energy of 1.02 eV, as compared to 0.89 eV for the surface exchange coefficients in the temperature range from 300 to 670 °C. Inhomogeneity was observed in the distribution of the oxygen-18 isotopic fraction from grain to grain in the ceramic samples, which was attributed to anisotropy in the diffusion and exchange of oxygen. By the use of a novel combination of electron back scattered diffraction measurements, time-of-flight, and focused ion beam SIMS, this anisotropy was confirmed by in-depth analysis of single grains of known orientation in a ceramic sample exchanged at 300 °C. Diffusion was shown to be faster in a grain oriented with the surface normal close to 100 and 010 (ab-plane oriented) than a grain with a surface normal close to 001 (c-axis oriented). The magnitude of this anisotropy is estimated to be close to a factor of 4, but this is only a lower bound due to experimental limitations. These findings are consistent with recent molecular dynamic simulations of this material where anisotropy in the oxygen transport was predicted.

Superior electrochemical performance and oxygen reduction kinetics of layered perovskite PrBa x Co 2 O 5+δ ( x = 0.90–1.0) oxides as cathode materials for intermediate-temperature solid oxide fuel cells

“…Fig. 1 shows the XRD patterns of as-prepared PB x CO (x ¼ 0.90e1.0) powder at room temperature, indexed to an orthorhombic superstructure with doubled c-axis, as a z a p , b z a p , c z 2a p (a p : the cell parameter of the primitive perovskite), which is consistent with Kilner's reports [12]. The XRD patterns of PB x CO collected at room temperature are correctly refined in the Pmmm space group (S. G.) derived from PBCO.…”

Defect formation in double perovskites PrBaCo2−xCuxO5+δ at elevated temperatures

“…Indeed, exactly this mechanism has been visualized by in-situ high-temperature neutron powder diffraction studies [19]. Notice also that the activation energy E a for oxygen tracer diffusion coefficient D* is found to be about 98.4 kJ/mol [43]. This value is somewhat smaller compared to the obtained disordering enthalpy 127 kJ/mol for reaction (1), Table 2.…”

“…This value is somewhat smaller compared to the obtained disordering enthalpy 127 kJ/mol for reaction (1), Table 2. The difference can be explained as due to lower temperature range (below 700°С) used in [43] where according to our calculations the concentration of oxygen vacancies V O2 in PrBaCo 2 O 5+δ is negligibly small. Therefore, the probability for the O3 oxygen ion to have a neighboring vacancy V O2 available for O3-O2 jump is to be very small also.…”

Impact of doping on the ionic conductivity of ceria: A comprehensive model

“…5,6 Presently, there are numerous candidate oxides which are considered for cathode and electrolyte applications for the next generation of intermediate temperature solid oxide fuel cells. [7][8][9][10][11][12] In previous studies of reduced CeO 2 , 13 charge transport was demonstrated to be achieved by a hopping process of O vacancies and the related distortions. This mechanism is in agreement with the O defect model established by careful measurements of the electrical conductivity of reduced CeO 2 as a function of temperature and O 2 pressure in Ref.…”