| 1. |
- Koemets, E., et al.
(författare)
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Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2
- 2021
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:10
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Tidskriftsartikel (refereegranskat)abstract
- Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe(2)O(3) and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mossbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory + dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites.
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| 2. |
- Golosova, N. O., et al.
(författare)
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Magnetic and structural properties of FeCO3 at high pressures
- 2017
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:13
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Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of siderite FeCO3 have been studied by means of neutron powder diffraction at pressures up to 7.5 GPa and first-principles theoretical calculations. The lattice compression in the rhombohedral calcite-type structure is dominated by the reduction of the Fe-O bonds, while the changes of the C-O bonds are much less pronounced. The Neel temperature of the antiferromagnetic ( AFM) ground state increases substantially under pressure with a coefficient dT(N)/dP = 1.8K/GPa, which is about 1.5 times larger in comparison with those predicted by the empirical Bloch rule. The ab initio calculations were performed in the framework of the density functional theory including Hubbard-U correction. The calculated structural parameters and Neel temperature as functions of pressure provide a reasonable agreement with the experimental results. The analysis of the density of electronic states points toward increased covalent bonding between the Fe and O atoms upon pressure, giving rise to unexpectedly large pressure coefficient of the Neel temperature and reduced ordered magnetic moments of Fe atoms.
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| 3. |
- Potapkin, V., et al.
(författare)
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Magnetic interactions in NiO at ultrahigh pressure
- 2016
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Ingår i: PHYSICAL REVIEW B. - : AMER PHYSICAL SOC. - 2469-9950. ; 93:20, s. 201110-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.
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