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- Greenberg, Eran, et al.
(author)
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Pressure-Induced Site-Selective Mott Insulator-Metal Transition in Fe2O3
- 2018
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In: Physical Review X. - : AMER PHYSICAL SOC. - 2160-3308. ; 8:3
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Journal article (peer-reviewed)abstract
- We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in Fe2O3 characterized by site-selective delocalization of the electrons. Density functional plus dynamical mean field theory (DFT + DMFT) calculations, along with Mossbauer spectroscopy, x-ray diffraction, and electrical transport measurements on Fe2O3 up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by ((FE3+HS)-F-VI)(2)O-3 [R (3) over barc structure]-amp;gt;(50) (GPa) (Fe-VIII(3+HS) Fe-VI(M))O-3 [P2(1)/n structure]-amp;gt;(68 Gpa)(Fe-VI(M))(2)O-3[Aba2/PPv structure]. Within the P2(1)/n crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions (Fe3+) and ions having delocalized electrons (Fe-M), and only at higher pressures is a fully metallic high-pressure structure obtained, all at room temperature. Thereby, the transition is characterized by delocalization/metallization of the 3d electrons on half the Fe sites, with a site-dependent collapse of local moments. Above approximately 50 GPa, Fe2O3 is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m*/m similar to 4 and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition (Fe-VIII(3+HS) Fe-VI(M))O-3 -amp;gt;(50) (GPa)(Fe-VIII(3+HS) Fe-VI(3+HS))O-3 within the same P2(1)/n structure, indicating a decoupling of the electronic and lattice degrees of freedom. Our results offer a model for understanding insulator-metal transitions in correlated electron materials, showing that the interplay of electronic correlations and crystal structure may result in rather complex behavior of the electronic and magnetic states of such compounds.
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- Leonov, Ivan, et al.
(author)
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Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures
- 2019
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In: npj Computational Materials. - : SPRINGERNATURE. - 2057-3960. ; 5
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Journal article (peer-reviewed)abstract
- The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earths lower mantle. Its high pressure-temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earths interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe-3 +/-delta and delta similar to 0.05-0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of similar to 200-250 GPa, i.e., sufficiently above the core-mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earths lower mantle.
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- Xu, Weiming M., et al.
(author)
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Pressure-induced hydrogen bond symmetrization in iron oxyhydroxide
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:17
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Journal article (peer-reviewed)abstract
- Under high pressures the hydrogen bonds were predicted to transform from a highly asymmetric soft O-H center dot center dot center dot O to a symmetric rigid configuration in which the proton lies midway between the two oxygen atoms. Despite four decades of research on hydroxyl containing compounds, pressure induced hydrogen bond symmetrization remains elusive. Following single crystal x-ray diffraction, Mossbauer and Raman spectroscopy measurements supported by ab initio calculations, we report the H-bonds symmetrization in iron oxyhydroxide, FeOOH, resulting from the Fe3+ high-to-low spin crossover at above 45 GPa.
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