Local structure and spin transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Fe</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>hematite at high pressure

Sanson, Andrea; Kantor, Innokenty; Cerantola, Valerio; Irifune, Tetsuo; Carnera, A.; Pascarelli, S.

doi:10.1103/physrevb.94.014112

Cited by 36 publications

(43 citation statements)

References 35 publications

(51 reference statements)

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“…Similar behavior has been observed in hematite, where the origin of this HS-LS transition has been the subject of multiple discussions 56,57 . In the present case, the nature of the volume collapse in ε-Fe 2 O 3 is properly explained by the local structural change around Fe atoms leading to a new phase of epsilon Fe 2 O 3 .…”

Section: Discussionsupporting

confidence: 71%

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

Sans¹,

Monteseguro²,

Garbarino³

et al. 2018

Nat Commun

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Iron oxides are among the major constituents of the deep Earth’s interior. Among them, the epsilon phase of Fe2O3 is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local environment of the tetrahedrally coordinated iron towards an octahedral coordination, finding evidence for a different iron oxide polymorph.

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Section: Discussionsupporting

confidence: 71%

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

Sans¹,

Monteseguro²,

Garbarino³

et al. 2018

Nat Commun

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“…Since the preedge feature is sensitive to the t 2g and e g components of the 3d band through hybridization effects, it is directly connected to the population of the HS and LS spin states. Here modifications in the preedge and edge XANES features between 33 and 39 GPa at ambient temperature show similarities with data collected upon the Fe spin transition in Fe 2 O 3 ( Figure S3; Badro et al, 2002;Mao et al, 1996;Narygina et al, 2009;Sanson et al, 2016;Wang et al, 2010). Therefore, we attribute the modifications of the preedge observed in this pressure range to the pressure-induced iron spin-crossover in α-FeOOH.…”

Section: Compression At Ambient Temperature Of α-Feoohsupporting

confidence: 81%

Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

Boulard

Harmand

Guyot

et al. 2019

Geophysical Research Letters

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Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite‐type FeO2 and FeO2Hx phases stable at deep terrestrial lower mantle pressures and temperatures. In the present study, we probed the iron oxidation state in high‐pressure transformation products of Fe3+OOH goethite by in situ X‐ray absorption spectroscopy in laser‐heated diamond‐anvil cell. At pressures and temperatures of ~91 GPa and 1,500–2,350 K, respectively, that is, in the previously reported stability field of FeO2Hx, a measured shift of −3.3 ± 0.1 eV of the Fe K‐edge demonstrates that iron has turned from Fe3+ to Fe2+. We interpret this reductive valence change of iron by a concomitant oxidation of oxygen atoms from O2− to O−, in agreement with previous suggestions based on the structures of pyrite‐type FeO2 and FeO2Hx phases. Such peculiar chemistry could drastically change our view of crystal chemistry in deep planetary interiors.

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“…Furthermore, it was reported [37] that the system reverses, as a function of time, from the LS to the HS state within the HP crystal structure. However, in more recent studies (e.g., Sanson et al [38]), the opposite was advocated, namely, that the electronic transition drives the structural transition. In addition, recent density-functional theory þ dynamical mean-field theory (DFT þ DMFT [39]) calculations predict that the electronic transition occurs within the hematite phase [40], i.e., prior to the structural transition, at a high compression of V < 0.8V 0 (V 0 is the equilibrium unit-cell volume), which, according to an experimental equation of state (EOS), e.g., Refs.…”

Section: Introductionmentioning

confidence: 99%

Pressure-Induced Site-Selective Mott Insulator-Metal Transition inFe2O3

et al. 2018

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We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in Fe 2 O 3 characterized by site-selective delocalization of the electrons. Density functional plus dynamical meanfield theory (DFT þ DMFT) calculations, along with Mössbauer spectroscopy, x-ray diffraction, and electrical transport measurements on Fe 2 O 3 up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by ð VI Fe 3þHS Þ 2 O 3 ½R3c structure! 50 GPa ð VIII Fe 3þHS VI Fe M ÞO 3 ½P2 1 =n structure! 68 GPa ð VI Fe M Þ 2 O 3 ½Aba2=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 (Fe 3þ) 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, Fe 2 O 3 is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m Ã =m ∼ 4 and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition ð VIII Fe 3þHS VI Fe M ÞO 3 ! 50 GPa ð VIII Fe 3þHS VI Fe 3þHS ÞO 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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Local structure and spin transition inFe2O3hematite at high pressure

Cited by 36 publications

References 35 publications

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

Pressure-Induced Site-Selective Mott Insulator-Metal Transition inFe2O3

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