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Ba7Nb4MoO20: A Proton or Oxide Ion Conductor?
Sara Adeeba Ismail1, Kazuaki Toyoura2, Lulu Jiang1
1College of Energy, Soochow University, No 1 Shizi Street, Gusu District, Suzhou 215006, China.
Ba7Nb4MoO20 is a pure oxide ion conductor, not a proton conductor. Hydration can enhance oxide ion conductivity at higher temperatures by releasing ions.
Area of Science:
- Solid-state chemistry
- Materials science
- Ion conduction
Background:
- Ba7Nb4MoO20 is a promising fast oxide ion conductor.
- Previous studies suggested proton conduction in humid atmospheres, conflicting with new findings.
Purpose of the Study:
- To clarify the conduction mechanism in Ba7Nb4MoO20 under varying humidity.
- To investigate the role of hydration on ionic conductivity.
Main Methods:
- Theoretical calculations to assess proton mobility.
- Electromotive force (EMF) measurements up to 800 °C.
- Analysis of H2O/D2O isotope effects.
Main Results:
- Theoretical and experimental evidence shows minimal proton mobility.
- Ba7Nb4MoO20 exhibits predominantly oxide ion conduction.
- Hydration stabilizes interstitial oxide ions, initially reducing conductivity (<400 °C).
- Above 400 °C, hydration enhances oxide ion conductivity by facilitating proton injection and releasing oxide ions.
Conclusions:
- Ba7Nb4MoO20 is confirmed as a near-pure oxide ion conductor.
- Hydration plays a complex role, potentially enhancing oxide ion conduction at elevated temperatures.
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