Strukturelle und elektronische Untersuchungen am hoch sauerstoffdefizitären Mischleiter Ba x Sr 1-x Co 0,8 Fe 0,2 O 3-delta (BSCF)
type: CreativeWork
description: Oxides of the perovskite structure as BSCF are well known for their ability to accommodate large deviations from the ideal stoichiometry of a perovskite ABO3. This leads to many interesting properties of these materials, such as superconductivity and high oxygen permeability, whereas these properties are also highly dependent on the surrounding oxygen partial pressure and temperature. In this family of materials, BSCF stands out as it accommodates an extremely high oxygen nonstoichiometry delta which leads to one of the highest oxygen permeation rate know thus far. This makes BSCF a promising candidate for industrial application as material for oxygen separation membranes. Unfortunately, BSCF tends to decompose into a hexagonal polymorph of the perovskite structure at typical application temperatures of 800°C, which could pose problems for an long term industrial application. In this work, two central questions were tackled: On the one hand, the question how the electronic compensation of the oxygen nonstoichiometry is achieved, on the other hand the nature of the decomposition of BSCF into a hexagonal phase. The electronic compensation was investigated by means of in situ X-Ray Absorption Spectroscopy, where the valence states of Co and Fe were determined as a function of oxygen partial pressure and temperature. It has been found that the charge compensation of the high oxygen nonstoichiometry is mainly achieved by the reduction of Co, and the further dependence of the valence states on temperature and oxygen partial pressure is very complex. Additionally it has been found that the charge compensation of the charge left behind by removed oxygen is not only done be reduction of the B-site cations Co and Fe, but also that the valence of oxygen changes during that process. A semiempiric band structure model has been suggested to describe this behaviour. The decomposition of BSCF has been investigated by means of X-Ray Diffraction and Electron Microscopy. The quantitat…
abstract: Oxides of the perovskite structure as BSCF are well known for their ability to accommodate large deviations from the ideal stoichiometry of a perovskite ABO3. This leads to many interesting properties of these materials, such as superconductivity and high oxygen permeability, whereas these properties are also highly dependent on the surrounding oxygen partial pressure and temperature. In this family of materials, BSCF stands out as it accommodates an extremely high oxygen nonstoichiometry delta which leads to one of the highest oxygen permeation rate know thus far. This makes BSCF a promising candidate for industrial application as material for oxygen separation membranes. Unfortunately, BSCF tends to decompose into a hexagonal polymorph of the perovskite structure at typical application temperatures of 800°C, which could pose problems for an long term industrial application. In this work, two central questions were tackled: On the one hand, the question how the electronic compensation of the oxygen nonstoichiometry is achieved, on the other hand the nature of the decomposition of BSCF into a hexagonal phase. The electronic compensation was investigated by means of in situ X-Ray Absorption Spectroscopy, where the valence states of Co and Fe were determined as a function of oxygen partial pressure and temperature. It has been found that the charge compensation of the high oxygen nonstoichiometry is mainly achieved by the reduction of Co, and the further dependence of the valence states on temperature and oxygen partial pressure is very complex. Additionally it has been found that the charge compensation of the charge left behind by removed oxygen is not only done be reduction of the B-site cations Co and Fe, but also that the valence of oxygen changes during that process. A semiempiric band structure model has been suggested to describe this behaviour. The decomposition of BSCF has been investigated by means of X-Ray Diffraction and Electron Microscopy. The quantitat…
author: Müller, David Nikolaus
language: ger
keywords: info:eu-repo/classification/ddc/540, Gemischter Leiter, Röntgenabsorption, Perowskit, Röntgenbeugung, Chemie, perovskite, oxygen separation membrane, X-ray absorption, X-ray diffraction
date published: 2010
date modified: 2026-07-30T19:43:35Z
provider: RWTH Aachen University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Publikationsserver der RWTH Aachen University