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arXiv · 1408.5551

Formation of Stoichiometric CsF$_n$ Compounds

Qiang Zhu·Artem R. Oganov·Qingfeng Zeng
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Abstract

Alkali halides $MX$, have been viewed as typical ionic compounds, characterized by 1:1 ratio necessary for charge balance between M$^+$ and X$^-$. It was proposed that group I elements like Cs can be oxidized further under high pressure. Here we perform a comprehensive study for the CsF-F system at pressures up to 100 GPa, and find extremely versatile chemistry. A series of CsF$_n$ ($n$ $\geq$ 1) compounds are predicted to be stable already at ambient pressure. Under pressure, 5$p$ electrons in Cs atoms become active, with growing tendency to form Cs$^{3+}$ and Cs$^{5+}$ valence states at fluorine-rich conditions. Although Cs$^{2+}$ and Cs$^{4+}$ are not energetically favoured, the interplay between two mechanisms (polyfluoride anions and polyvalent Cs cations) allows CsF$_2$ and CsF$_4$ compounds to be stable under pressure. The estimated defluorination temperatures of CsF$_n$ (n=2,3,5) compounds at atmospheric pressure (218 $^\circ$C, 150 $^\circ$C, -15 $^\circ$C, respectively), are attractive for fluorine storage applications.

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Qiang Zhu, Artem R. Oganov, Qingfeng Zeng. 2014-08-24. Formation of Stoichiometric CsF$_n$ Compounds. https://doi.org/10.1038/srep07875

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