Oxygen thermodynamics and ion conductivity in the solid solution La1−xSrxCoO3−δ at large strontium content

Abstract

Abstract. The equilibrium oxygen content was measured in the model system and important oxygen permeable material Lal.xSrxCoO3. 6, where x = 0.6, in the temperature range 650-900 ~ and oxygen partial pressure range between 10 .5 and 1 atm. The data were utilized to obtain changes in the partial entropy and enthalpy of oxygen in the solid as a function of the oxygen content. It is shown that the initially cubic perovskite undergoes to a phase transition to a tetragonal structure at 8 > 0.3. The oxygen permeation of L0.4Sr0.6CoO3_ ~ at 700-900 ~ is found to be controlled by bulk solid state processes. The activation energy equals about 0.8 eV at high oxygen pressure and small oxygen nonstoichiometry. Increasing oxygen deficiency results in a rapid increase in the activation energy. In combination with thermodynamic data, these changes can be explained as resulting from the intrinsic, spatial inhomogeneouty in oxygen vacancy distribution which varies both with temperature and oxygen nonstoichiometry. It is shown that, when the oxygen deficiency increases at constant temperature, the oxygen vacancies form locally ordered microdomains (clusters), which eventually results in a transition of the cubic perovskite structure to the tetragonal structure. The oxygen ion conductivity depends strongly on the development of the ordering.

High-temperature order-disorder transition and polaronic conductivity inPrBaCo2O5.48

“…The oxygen disorder above T OD can also favor ionic conductivity due to random redistribution of the structural vacancies over the O3 and O4 positions, as shown for certain perovskite systems. [15][16][17][18][19]33 A similar effect was found in layered ferrites Sr 3 Fe 2 O 6−␦ , where disordering of the FeO 5 pyramides results in a rapid increase of the ionic conductivity. 33 Further studies of the ionic conductivity are necessary to clarify this issue.…”

“…Ionic conductivity in cobaltites was first observed in 1991 by Teraoka 14 in La 0.6 Sr 0.4 Co 0.8 B 0.2 O 3−␦ ͑B = Fe, Co, Ni, Cu͒ and it is believed that oxygen orderdisorder phenomena play an important role for its occurrence. [15][16][17][18][19] Since no information exists about the high-temperature structures of layered cobaltites, we decided to investigate PrBaCo 2 O 5.48 by means of neutron powder diffraction ͑NPD͒. This is a powerful technique for structure determination, which provides reliable infomation on the oxygen ion positions and occupancies.…”

Electrical Properties of the Ferrite SrFeOy at High Temperatures

“…2 and 5). The observed decrease in the ion conductivity may be related to partial trapping of oxygen vacancies in local clusters (e.g., Fe Fe < O G Fe Fe ), which are known in perovskite-related oxides (10,11). Certainly, in general, an increase in temperature results in the respective increase in the total amount of oxygen vacancies and, thus, an increase in the ion conductivity.…”

Defect equilibria and partial molar properties of (La,Sr)(Co,Fe)O3−

“…Further, the authors pointed out linear relations between the enthalpy of oxidation and the concentration of the A-site substituent x, for a given M. Partial molar properties of oxygen have been reported, e.g. for La 1−x Sr x CoO 3−δ [23,24] [27,28]. X-ray diffraction and neutron diffraction were performed for structural characterization and to ensure the phase purity of the perovskite samples.…”