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Persistent URL http://purl.org/net/epubs/work/63242720
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Record Id 63242720
Title Redox Stability and Ionic Conduction in Donor-Substituted LaNbO4 under Hydrogen Environments
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Abstract Fergusonite-scheelite type LaNbO4-based materials have presented promising potential for development as oxygen ionic or protonic conductors for solid oxide fuel cell (SOFC) and electrolysis cell (SOEC) applications. Among these material candidates, W- and Mo-substituted LaNbO4 show acceptable oxygen ion conductivity and excellent chemical stability under atmospheric conditions. However, the properties and performances of these materials under reducing atmospheres remain unclear. Exploring W- and Mo-substituted LaNbO4 under reducing atmospheres, especially under hydrogen conditions, is crucial for future SOFC/SOEC applications. Therefore, this work aims to investigate the structural and redox stabilities of W- and Mo-substituted LaNbO4 under hydrogen conditions and their corresponding changes in transport properties. The crystal structure of W-substituted LaNbO4 is found to remain stable, while the structural symmetry of Mo-substituted LaNbO4 is significantly reduced after hydrogen treatments. Multiple techniques have been used to attribute this difference in structural evolution to the redox stability of W cations and the instability of Mo cations under hydrogen conditions. X-ray absorption fine structure (XAFS) studies uncover the profound correlation between the crystal structure, the local coordination environment, and the oxidation state of cations. The neutron Compton scattering studies further provide a kinetic description of the elements. The conductivity of both materials increases significantly under hydrogen conditions. The transport number of different charge species indicates the conductivity enhancement via distinct mechanisms. The increase in conductivity in W-substituted LaNbO4 is attributed to proton incorporation and transport. Meanwhile, it has been confirmed that the increase in conductivity in Mo-substituted LaNbO4 is partially due to electronic conduction. Attempts have been made to probe the hydrogen content in both materials directly, but these have proved inclusive. However, proton diffusion has been determined directly for the first time in W-substituted LaNbO4 using isotope exchange and mass spectrometry techniques.
Organisation ISIS , ISIS-VESUVIO , STFC
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Language English (EN)
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Thesis PhD, Department of Materials, Imperial College London, 2025. 2025