March 2014Transition metal oxides and especially CeO2 are known for their ability to exchange oxygen with the surrounding gas atmosphere. This behaviour has significant impact on the electrical conductivity, and with decreasing p(O2) oxygen vacancies and electrons are formend by loss of oxygen. An alternative class of oxygen storage materials, namely mayenite (Ca12Al14O33, abbrev. C12A7:O), shows a cage structure formed by CaO and Al2O3 (see inset). Between these cages, oxygen ions are highly mobile at elevated temperature. The conductivity of this material is also affected by hydration, which depends on p(H2O) (humidity). The hydration of mayenite can be expressed as follows: Ca12Al14O33 + H2O → Ca12Al14O32(OH)2 At very high humidities the conductivity follows the relation lg σ ∝ lg p(H2O)^-1 whereas at low humidities it comes close to the pure oxygen ion conductivity. In terms of a defect chemical model the course of the conductivity vs. p(H2O) can be well explained. (Picture submitted by Jens-Peter Eufinger.) https://www.uni-giessen.de/en/faculties/f08/departments/physchem/janek/gallerypotm/pom2014/march-2014/viewhttps://www.uni-giessen.de/@@site-logo/logo.png
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March 2014
Transition metal oxides and especially CeO2 are known for their ability to exchange oxygen with the surrounding gas atmosphere. This behaviour has significant impact on the electrical conductivity, and with decreasing p(O2) oxygen vacancies and electrons are formend by loss of oxygen. An alternative class of oxygen storage materials, namely mayenite (Ca12Al14O33, abbrev. C12A7:O), shows a cage structure formed by CaO and Al2O3 (see inset). Between these cages, oxygen ions are highly mobile at elevated temperature. The conductivity of this material is also affected by hydration, which depends on p(H2O) (humidity). The hydration of mayenite can be expressed as follows: Ca12Al14O33 + H2O → Ca12Al14O32(OH)2 At very high humidities the conductivity follows the relation lg σ ∝ lg p(H2O)^-1 whereas at low humidities it comes close to the pure oxygen ion conductivity. In terms of a defect chemical model the course of the conductivity vs. p(H2O) can be well explained. (Picture submitted by Jens-Peter Eufinger.)
