Nonstoichiometric ferrites of alkaline and rare earth metals with perovskite-type structure АВО_3-δ, possess high mixed oxygen/electronic conductivity. Thus these systems are promising materials for solid oxide fuel cell electrodes, oxygen-permeable membranes for oxygen separation and catalysts for partial oxidation of hydrocarbons in catalytic membrane reactors. Using high-temperature X-ray diffraction La_1-xSr_xFeO_3-δ (0 ≤ x ≤ 1) solid solutions with perovskite-related structure were investigated. Samples with x≥0.6 were cubic modification of perovskite. Heating in air up to synthesis temperature (1200 ^oC) leaved the phase composition of the sample La_0.25Sr_0.75FeO_3-δ unaltered, in spite of high oxygen lost. Heating in vacuum led to significant broadening of diffraction peaks concerned with formation of two-phase region at about 900^oС. Adding a small quantity of Palmitic Acid to the sample resulted in decrease of phase transition temperature up to 600^oC and splitting of diffraction peaks. Following raise of temperature led to increase of the quantity of a new phase. The phase transition occured without changing of symmetry of unit cell. In vacuum at about 1000^oC the sample was mono-phase with cubic modification of perovskite structure. Following cooling down in vacuum up to 800^oC resulted in ordering of oxygen vacancies with the formation Grenier-type phase. Isosymmetrical phase transition was also observed for composition x=0.6. According to high-resolution synchrotron diffraction, significant broadening of diffraction peaks was mainly associated with the overlap of the diffraction peaks of two phases of the solid solutions with comparable lattice parameters, but not with the microstructure of the sample. Finally, under heating in air up to 1200^oC of the sample SrFeO_3-δ, perovskite structure was stable. However, at about 1200^oC additional diffraction peak at about 32^o (2θ) of low-intensity (about 10% from maximal intensity) was observed. Simulated diffraction pattern of defect model of perovskite and brownmillerite layers alternation in one dimension had a good agreement with the experiment.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/15318 must be provided.

1. In situ XRD investigation of Co₃O₄ reduction