Elusive Valence Transition in Mixed-Valence Sesquioxide Cs4O6

Colman RH, Okur HE, Kockelmann W, Brown CM, Sans A, Felser C, Jansen M, Prassides K (2019)

Publication Type: Journal article

Publication year: 2019

Journal

Inorganic Chemistry American Chemical Society

Book Volume: 58

Pages Range: 14532-14541

Journal Issue: 21

DOI: 10.1021/acs.inorgchem.9b02122

Abstract

Cs4O6 is a mixed-valence molecular oxide with a cubic structure, comprising valency-delocalized O2 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 O2 2- and O2 - 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 of the 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 O2 - units provides an intimate link between the crystal and magnetic properties of charge-ordered Cs4O6, naturally accounting for the absence of magnetic order.

Involved external institutions

Univerzita Karlova v Praze / Charles University in Prague CZ Czech Republic (CZ) Bursa Technical University / Bursa Teknik Üniversitesi TR Turkey (TR) Rutherford Appleton Laboratory GB United Kingdom (GB) National Institute of Standards and Technology (NIST) US United States (USA) (US) Max-Planck-Institut für Festkörperforschung DE Germany (DE) Osaka Prefecture University 大阪府立大学 JP Japan (JP) Max-Planck-Institut für Chemische Physik fester Stoffe (MPI CPfS) / Max Planck Institute for Chemical Physics of Solids DE Germany (DE)

How to cite

APA:

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

MLA:

Colman, Ross H., et al. "Elusive Valence Transition in Mixed-Valence Sesquioxide Cs4O6." Inorganic Chemistry 58.21 (2019): 14532-14541.

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