Cr<sup>3+</sup>-Containing Carbonates and Cr<sub>2</sub>O<sub>3</sub>-<i>Pbcn</i> at Extreme Conditions
We synthesized three carbonates, Cr<sub>2</sub>[CO<sub>3</sub>]<sub>3</sub>, Cr<sub>2</sub>[C<sub>2</sub>O<sub>5</sub>][CO<sub>3</sub>]<sub>2</sub>, and Cr<sub>2</sub>[CO<sub>3</sub>][O]<sub>2</sub>, containing Cr<sup>3+</sup> by laser heating of chromium oxides in CO<sub>2</sub> at pressures between 45 and 55 GPa. All phases were characterized by single-crystal X-ray diffraction and Raman spectroscopy, while density functional theory calculations complemented the experimental results. The structure of Cr<sub>2</sub>[CO<sub>3</sub>]<sub>3</sub>-<i>P</i>6<sub>3</sub>/<i>m</i> contains coplanar groups, and a 4<i>f</i> Wyckoff site is half occupied by Cr<sup>3+</sup>. Cr<sub>2</sub>[C<sub>2</sub>O<sub>5</sub>][CO<sub>3</sub>]<sub>2</sub>-<i>C</i>2/<i>c</i> is characterized by coplanar [CO3]2− and pyro-[C2O5]2− anions and is isostructural to Al<sub>2</sub>[C<sub>2</sub>O<sub>5</sub>][CO<sub>3</sub>]<sub>2</sub>. It was obtained only after prolonged laser heating. The oxycarbonate Cr<sub>2</sub>[CO<sub>3</sub>][O]<sub>2</sub>-<i>Pbcn</i> was synthesized at the highest pressure (55 GPa) studied here. In this structure, half of the oxygen atoms coordinate one carbon and two Cr atoms, while the other half coordinate three chromium atoms. The oxidation state of chromium in the carbonates is +3, independent of the oxidation state (+3 or +4) of chromium in the oxide starting material. We observed the transformation of Cr<sub>2</sub>O<sub>3</sub>-<i>R</i>3̅<i>c</i> to Cr<sub>2</sub>O<sub>3</sub>-<i>Pbcn</i> above 45(2) GPa after laser heating.
Publication Details
- Journal
- Figshare
- Published
- 2025-03-04
- DOI
- https://doi.org/10.1021/acs.inorgchem.4c05003.s001
- Primary Topic
- High-pressure geophysics and materials
- Type
- article
- Field-Weighted Citation Impact
- 0.00