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  Elusive Valence Transition in Mixed-Valence Sesquioxide Cs4O6

Colman, R. H., Okur, H. E., Kockelmann, W., Brown, C. M., Sans, A., Felser, C., et al. (2019). Elusive Valence Transition in Mixed-Valence Sesquioxide Cs4O6. Inorganic Chemistry, 58(21), 14532-14541. doi:10.1021/acs.inorgchem.9b02122.

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 Creators:
Colman, Ross H.1, Author
Okur, H. Esma1, Author
Kockelmann, Winfried1, Author
Brown, Craig M.1, Author
Sans, Annette1, Author
Felser, Claudia2, Author           
Jansen, Martin1, Author
Prassides, Kosmas1, Author
Affiliations:
1External Organizations, ou_persistent22              
2Claudia Felser, Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863429              

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 Abstract: Cs4O6 is a mixed-valence molecular oxide with a cubic structure, comprising valency-delocalized O-2(4/3-) units and with properties highly sensitive to cooling protocols. Here we use neutron powder diffraction to authenticate that, while upon deep quenching the cubic phase is kinetically arrested down to cryogenic temperatures, ultraslow cooling results in an incomplete structural transition to a contracted tetragonal phase. Two dioxygen anions in a 1:2 ratio are identified, providing evidence that the transition is accompanied by charge and orbital order and stabilizes a Robin-Day Class II mixed-valence state, comprising O-2(2-) and O-2(-) anions. The phenomenology of the phase change is consistent with that of a martensitic transition. The response of the low-temperature phase assemblage to heating is complex, involving a series of successive interconversions between the coexisting phases. Notably, a broad interconversion plateau is present near 260 K, signifying reentrant kinetic arrest tetragonal phase upon heating because of the combined effects of increased steric hindrance for molecular rotation and melting of charge and orbital order. The geometrically frustrated pyrochlore lattice adopted by the paramagnetic S = 1/2 O-2(-) units provides an intimate link between the crystal and magnetic properties of charge-ordered Cs4O6, naturally accounting for the absence of magnetic order.

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Language(s): eng - English
 Dates: 2019-10-212019-10-21
 Publication Status: Issued
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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 58 (21) Sequence Number: - Start / End Page: 14532 - 14541 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669