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| Hauptseite > Publikationsdatenbank > There is no Fe4+: What X-Ray spectroscopy can tell you about point defects (and what not) |
| Hauptseite > Publikationsdatenbank > There is no Fe4+: What X-Ray spectroscopy can tell you about point defects (and what not) |
| Conference Presentation (Invited) | FZJ-2020-04417 |
2020
Abstract: Charged point defects are an integral part of defect equilibria in solid state ionics, especially when reactions with a gas or liquid are involved. With the advent of X-ray spectroscopic methods made possible in atmospheres approaching ambient pressure and at elevated temperatures it has become tempting to observe these ions and their charge states directly as surface and bulk redox processes take place. Though with the right checks and balances this approach can give, and has given, invaluable insights into mechanisms governing electrochemical properties of solids and their interaction with gases and liquids, it has also led to many misconceptions. In this presentation, I will use prototypical materials such as (La,Sr)(Fe,Co)O3-δ and Sr(Ti,Co)O3-δ utilized in solid state electrochemistry to showcase the strengths and limitations of in situ X-Ray absorption (XAS) and photoemission spectroscopy (XPS). The secession from using XAS and XPS to (attempt to) simply determine formal oxidation states as a function of temperature, chemistry and atmosphere has, for example, led to recognition of the role of the transition metal in the perovskite structure in the former and peculiarities in the conductions mechanism of the latter compound.
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