Impact of Anion Vacancies on the Local and Electronic Structures of Iron-Based Oxyfluoride Electrodes

Mario Burbano, Mathieu Duttine, Benjamin Morgan, Olaf Borkiewicz, Karena Chapman, Alain Wattiaux, Henri Groult, Mathieu Salanne, Damien Dambournet

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The properties of crystalline solids can be significantly modified by deliberately introducing point defects. Understanding these effects, however, requires understanding the changes in geometry and electronic structure of the host material. Here we report the effect of forming anion vacancies, via dehydroxylation, in a hexagonal-tungsten-bronze–structured iron oxyfluoride, which has potential use as a lithium-ion battery cathode. Our combined pairdistribution function and density-functional–theory analysis indicates that oxygen vacancy formation is accompanied by a spontaneous rearrangement of fluorine anions and vacancies, producing dual pyramidal (FeF4)–O–(FeF4) structural units containing five-fold–coordinated Fe atoms. The addition of lattice oxygen introduces new electronic states above the top of the valence band, with a corresponding reduction in the optical band gap from 4.05 eV to 2.05 eV. This band gap reduction relative to the FeF3 parent material is correlated with a significant improvement in lithium insertion capability relative to defect-free compound.
Original languageEnglish
Pages (from-to)107-112
Number of pages6
JournalJournal of Physical Chemistry Letters
Issue number1
Early online date19 Dec 2018
Publication statusPublished - 3 Jan 2019

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry


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