In:
Small Methods, Wiley, Vol. 5, No. 10 ( 2021-10)
Abstract:
Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn 3 O 4 to Mn 2 O 3 limits efficiency. In contrast, (Mn 1− x Fe x ) 3 O 4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe‐doped Mn oxides is performed to elucidate how Fe incorporation influences solid‐state transformations. X‐ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high‐resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe‐enriched crystallites likely correspond to jacobsite. In situ X‐ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn 2+ in the spinel phase to Mn 3+ in bixbyite. Extended X‐ray absorption fine structure shows that FeO length is larger than MnO, but both electron energy loss spectroscopy and X‐ray absorption near edge structure indicate that iron is always present as Fe 3+ in octahedral sites. These structural modifications may facilitate ionic diffusion during bixbyite formation.
Type of Medium:
Online Resource
ISSN:
2366-9608
,
2366-9608
DOI:
10.1002/smtd.202100550
Language:
English
Publisher:
Wiley
Publication Date:
2021
detail.hit.zdb_id:
2884448-8
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