Verwey-Type Charge Ordering and Site-Selective Mott Transition in Fe4O5under Pressure

The metal-insulator transition driven by electronic correlations is one of the most fundamental concepts in condensed matter. In mixed-valence compounds, this transition is often accompanied by charge ordering (CO), resulting in the emergence of complex phases and unusual behaviors. The famous example is the archetypal mixed-valence mineral magnetite, Fe3O4, exhibiting a complex charge-ordering below the Verwey transition, whose nature has been a subject of long-time debates. In our study, using high-resolution X-ray diffraction supplemented by resistance measurements and DFT+DMFT calculations, the electronic, magnetic, and structural properties of recently synthesized mixed-valence Fe4O5are investigated under pressure to ∼100 GPa. Our calculations, consistent with experiment, reveal that at ambient conditions Fe4O5is a narrow-gap insulator characterized by the original Verwey-type CO. Under pressure Fe4O5undergoes a series of electronic and magnetic-state transitions with an unusual compressional behavior above ∼50 GPa. A site-dependent collapse of local magnetic moments is followed by the site-selective insulator-to-metal transition at ∼84 GPa, occurring at the octahedral Fe sites. This phase transition is accompanied by a 2+ to 3+ valence change of the prismatic Fe ions and collapse of CO. We provide a microscopic explanation of the complex charge ordering in Fe4O5which "unifies" it with the behavior of two archetypal examples of charge- or bond-ordered materials, magnetite and rare-earth nickelates (RNiO3). We find that at low temperatures the Verwey-type CO competes with the "trimeron"/"dimeron" charge ordered states, allowing for pressure/temperature tuning of charge ordering. Summing up the available data, we present the pressure-temperature phase diagram of Fe4O5 © 2022 American Chemical Society. All rights reserved.EAR-1634415; National Science Foundation, NSF: EAR-1606856; U.S. Department of Energy, USDOE: DE-FG02-94ER14466; Office of Science, SC; Argonne National Laboratory, ANL: DE-AC02-06CH11357; Deutsche Forschungsgemeinschaft, DFG: OV-110/3-2; Russian Foundation for Basic Research, РФФИ: 20-42-660027; Israel Science Foundation, ISF: 1552/18, 1748/20; Russian Science Foundation, RSF: 19-72-30043; 122021000039-4We thank L. S. Dubrovinsky, I. A. Abrikosov, and V. Prakapenka for their interest in this research and B. Lavina for fruitful discussions about in situ DAC synthesis. We are grateful to M. Hanfland for the assistance in using beamline ID-15B of ESRF, Grenoble, France. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation-Earth Sciences (Grant EAR-1634415) and Department of Energy-GeoSciences (Grant DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Use of the COMPRES-GSECARS gas loading system was supported by COMPRES under NSF Cooperative Agreement EAR-1606856 and by GSECARS through NSF Grant EAR-1634415 and DOE Grant DE-FG02-94ER14466.The work was partly supported by the Israel Science Foundation (Grants No. 1552/18 and 1748/20) and the Deutsche Forschungsgemeinschaft Grant No. OV-110/3-2. The theoretical analysis was supported by Russian Foundation for the Basic Research (Project No. 20-42-660027). The DFT calculations were supported by the state assignment of Minobrnauki of Russia (Theme “Electron” No. 122021000039-4). The DFT+DMFT calculations were supported by the Russian Science Foundation (Project No. 19-72-30043)

A summary of ODP leg 141 hydrogeologic, geochemical and thermal results

The subduction of the oceanic spreading center at the Chile Triple Junction is marked by a substantial thermal perturbation and marked changes in the hydrogeologic and aqueous geochemical regimes in the overthrust plate. Ridge subduction substantially changes the fluid chemistry in the wedge through variably hydrating the oceanic basement, accretionary wedge, and continental backstop. This generates positive anomalies in salinity and chloride values with respect to sea water. The wedge immediately above the subducted ridge also experiences greatly enhance diagenesis and cementation together with the influx of primordial mantle derived ⁴He. Linear temperature and pore fluid chemistry profiles suggest a predominantly diffusive/conductive regime predominates in the interior eastern portion of the wedge and continental backstop region. In contrast, a vigorous and transient hydrogeolgic system within 5 km of the toe of the wedge at both Sites 859 and 863 generates spatially narrow, large, and complex anomalies in temperature and fluid chemistry. At the toe the vigorous hydrogeologic system may be variably influenced by the episodic expulsion of fluid from both the deeper parts of the wedge and oceanic basement driven convection systems. Structural and diagenetic observations are also consistent with a hydrogeologic regime that both evolves with time and that is dominated by episodic processes. In particular, studies of cements, mineralized veins, deformation bands, and Fe sulfide distribution suggest that above the subducting ridge (i.e., Site 863) the lithification in the wedge is greatly enhanced and that and periods of enhanced fluid expulsion are associated with local hydrofracture and dilation episodes

Effect of chemistry on the compressibility of silicate perovskite in the lower mantle

Three single-crystals of magnesium silicate perovskite with differing chemical compositions have been studied by means of synchrotron X-ray diffraction in diamond anvil cells with He as pressure transmitting medium from room pressure up to 75GPa. In addition to the end-member MgSiO 3 composition, a perovskite containing 4mol% of the Fe 2+SiO 3 component [(Mg,Fe)SiO 3] and one containing 37mol% of an Fe 3+AlO 3 component [(Mg,Fe)(Al,Si)SiO 3] were investigated. The high-quality of the collected data allows a detailed examination of the effect of different chemical substitutions on the compression mechanism of perovskite and on its equation of state (EoS). The bulk modulus and first pressure derivative determined for MgSiO 3 perovskite obtained by fitting a 3rd-order Birch-Murnaghan are found to be quite insensitive to the maximum pressure to which the data are fitted. The EoS parameters obtained by fitting data from room pressure to 10, 40 or 75GPa are almost identical. This is not the case, however, for either (Mg,Fe)SiO 3 or (Mg,Fe)(Al,Si)SiO 3 perovskites, for which volumes calculated from an EoS obtained from fitting data up to 40GPa deviate from the experimental data above 40GPa. In the case of (Mg,Fe)SiO 3 perovskite this deviation appears to be related to a change in octahedral tilting during compression, as revealed by analysis of the lattice strain variation with pressure. The tilting change is a likely consequence of a high-spin to intermediate spin transition of Fe 2+ but the effect on the density and bulk modulus is almost negligible and unlikely to cause seismically observable changes in the mantle. In the case of (Mg,Fe)(Al,Si)SiO 3 perovskite, the deviation is clearly due to a change in the compressibility of the c-axis and no evidence for effects due to a change in Fe spin state is observed. Substitution of Fe 2+SiO 3 has a significant negative effect on the bulk sound velocity while increasing density, whereas the effect of Fe 3+AlO 3 substitution on both the bulk sound velocity and density are in the same direction but more modest. The latter substitution may, therefore, be more compatible with some aspects of seismic anomalies observed at the base of the lower mantle

Seismically invisible water in Earth's transition zone?

Ringwoodite, the dominant mineral at depths between 520 km and 660 km, can store up to 2–3 wt.% of water in its crystal structure, making the Earth's transition zone a plausible water reservoir that plays a central role in Earth's deep water cycle. Experiments show that hydration of ringwoodite significantly reduces elastic wave velocities at room pressure, but the effect of pressure remains poorly constrained. Here, a novel experimental setup enables a direct quantification of the effect of hydration on ringwoodite single-crystal elasticity and density at pressures of the Earth's transition zone and high temperatures. Our data show that the hydration-induced reduction of seismic velocities almost vanishes at conditions of the transition zone. Seismic data thus agree with a wide range of water contents in the transition zone

Plymorphism of walleye pollock gadus chalcogrammus mitochondrial DNA control region in the asiatic part of the range and its phylogeographic history

The phylogeographic analysis of Gadus chalcogrammus from the Asian part of the range (the western part of the Bering Sea, the Sea of Okhotsk and the Sea of Japan, the Pacific waters of the Kuril Islands and Kamchatka) based on data on the polymorphism of the mtDNA control region fragment (D-loop, 526 bp) was performed for the first time using large-scale material (1162 individuals from 38 samples). The obtained results indicate the existence of two large groups in the surveyed water area: one is localized in the western part of the Bering Sea, and the other is formed by samples from the Sea of Japan and the Sea of Okhotsk and from the Pacific waters of the Kuril Islands and Kamchatka. An unusually low level of polymorphism in the mtDNA control region of Gadus chalcogrammus was revealed, which was also previously found in G. macrocephalus and is probably due to similar microevolutionary processes that took place in the past in both species

The effect of the intermolecular potential formulation on the state-selected energy exchange rate coefficients in N2-N2 collisions

15 pags.; 12 figs.; 2 tabs.The rate coefficients for N2-N2 collision-induced vibrational energy exchange (important for the enhancement of several modern innovative technologies) have been computed over a wide range of temperature. Potential energy surfaces based on different formulations of the intramolecular and intermolecular components of the interaction have been used to compute quasiclassically and semiclassically some vibrational to vibrational energy transfer rate coefficients. Related outcomes have been rationalized in terms of state-to-state probabilities and cross sections for quasi-resonant transitions and deexcitations from the first excited vibrational level (for which experimental information are available). On this ground, it has been possible to spot critical differences on the vibrational energy exchange mechanisms supported by the different surfaces (mainly by their intermolecular components) in the low collision energy regime, though still effective for temperatures as high as 10,000 K. It was found, in particular, that the most recently proposed intermolecular potential becomes the most effective in promoting vibrational energy exchange near threshold temperatures and has a behavior opposite to the previously proposed one when varying the coupling of vibration with the other degrees of freedom. © 2014 Wiley Periodicals, Inc.Contract grant sponsor: Spanish MEC;Contract grant number : CTQ2008-02578, CTQ2009-07647, 2009S GR104,CTQ2012-37404, FIS2010-22064-C02-02 and CSD2009-00038Peer Reviewe