Oxygen-poor Conditions Research Articles

Redrawing the early sulfur cycle

The Archaean atmosphere may have been well oxygenated, according to a reconsideration of sulfur cycling at that time. This challenges the view that sedimentary sulfur records oxygen-poor conditions during Earth’s first two billion years.

Radionuclide incorporation in negative thermal expansion [formula omitted]-Zr(WO4)2: A density functional theory study

The incorporation of uranium, plutonium and technetium in the negative thermal expansion (NTE) α-Zr(WO4)2 has been investigated within the framework of density functional theory (DFT). It is found that the vacancy formation energies of the charged vacancies are overall larger than that of its counterpart neutral Frenkel defects and Schottky defects. DFT calculations suggest that U and Pu substitutions for the Zr site are preferred in α-Zr(WO4)2. In case of Tc substitution, both Tc(IV) for the Zr site and Tc(VII) for the W site are considered under oxygen-poor and oxygen-rich conditions, while Tc(VII) substitution can be improved significantly by including Y2O3 (charge compensation).

Estrogen and estrogen receptor affects MMP2 and MMP9 expression through classical ER pathway and promotes migration of lower venous vascular smooth muscle cells.

To explore the role of estrogen and estrogen receptors in the migration of vascular smooth muscle cells in varicose lower-extremity veins. Tissue samples of normal lower extremity vein (56 cases) and varicose lower extremity vein (47 cases) were collected. Western blot and real-time fluorescent qPCR were performed to measure the expression of Estrogen receptor α (ERα) in tissues. Two cell co-culture systems were established for human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs). One system was incubated under normal oxygen conditions (normal oxygen group), and the other was under oxygen-poor conditions (hypoxia group). The two systems were treated with 10-7 mM Estrogen E2, 10-7 mM BSA-conjugated Estrogen E2-BSA, 10-7 mM Estrogen E2+10-3 mM Tamoxifen (TAM), respectively for 24 h. The treated cells were subjected to cell scratch assay, transwell assay, and Western blot analysis of MMP2 and MMP9 protein expression. The expression of ERα in varicose lower extremity vein was significantly up-regulated compared with that in normal lower extremity vein. The cell migration rate and the number of migrating cells in untreated hypoxia group and E2-treated normal oxygen group were comparable (p>0.05) to those in untreated normal oxygen group. The cell migration rate and the number of migrating cells were significantly increased (p<0.05) in E2-treated hypoxia group, compared with E2-treated normal oxygen group and untreated hypoxia group. The cell migration rate, the number of migrating cells, and expression levels of MMP2 and MMP9 were significantly decreased in E2/TAM-treated hypoxia group, compared with those in E2-treated hypoxia group. In summary, E2 can promote the migration of vascular smooth muscle cells and induce varicose veins of the lower extremities, which may be related to the promotion of MMP2 and MMP9 expression through the classical pathway of ER.

Electron polarons and donor point defects in americium dioxideAmO2

Intrinsic donor point defects and electron polarons are investigated in bulk ${\mathrm{AmO}}_{2}$ using density functional theory $+U$ calculations. Oxygen vacancies are deep double-donor defects, with transition energy levels closer to the valence band maximum than to the conduction band minimum. Americium interstitials are unlikely, due to prohibitive formation energies. Self-trapped electron polarons (which locally correspond to reducing one ${\mathrm{Am}}^{4+}$ in ${\mathrm{Am}}^{3+}$) are found extremely stable (self-trapping energy $=\ensuremath{-}1.01\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$). The electron is even more stable in the self-trapped state (far from an oxygen vacancy) rather than in association with an oxygen vacancy, indicating that oxygen vacancies have the tendency to spontaneously ionize, and thus automatically liberate electron polarons in the lattice. This large stability of the electron polarons confines the accessible range of Fermi levels to a very narrow interval between the valence band maximum ${E}_{\text{VBM}}$ and $\ensuremath{\sim}{E}_{\text{VBM}}+0.09\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. In oxygen-poor conditions, oxygen vacancies may be formed in rather large concentration in ${\mathrm{AmO}}_{2}$ and have a strong probability to be doubly or singly ionized, with charge compensation being mostly ensured by a large number of electron polarons. The electron polaron hopping from an Am atom onto the nearest one involves a rather large activation energy of $\ensuremath{\sim}0.6\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ and probably takes place by a nonadiabatic mechanism.

Highly conductive and transparent gallium doped zinc oxide thin films via chemical vapor deposition

Degenerately doped ZnO is seen as a potential substitute to the ubiquitous and expensive Sn doped In2O3 as a transparent electrode in optoelectronic devices. Here, highly conductive and transparent Ga doped ZnO thin films were grown via aerosol assisted chemical vapor deposition. The lowest resistivity (7.8 × 10−4 Ω.cm) and highest carrier concentration (4.23 × 1020 cm−3) ever reported for AACVD grown ZnO: Ga was achieved due to using oxygen poor growth conditions enabled by diethylzinc and triethylgallium precursors.

On the mechanism of H2 activation over single-atom catalyst: An understanding of Pt1/WOx in the hydrogenolysis reaction

Owing to the atomic dispersion of active sites via electronic interaction with supports, single-atom catalysts (SACs) grant maximum utilization of metals with unique activity and/or selectivity in various catalytic processes. However, the stability of single atoms under oxygen-poor conditions, and the mechanism of hydrogen activation on SACs remain elusive. Here, through a combination of theoretical calculation and experiments, the stabilization of metal single atoms on tungsten oxide and its catalytic properties in H2 activation are investigated. Our calculation results indicate that the oxygen defects on the WO3(001) surface play a vital role in the stabilization of single metal atoms through electron transfer from the oxygen vacancies to the metal atoms. In comparison with Pd and Au, Pt single atoms possess greatly enhanced stability on the WOx(001) surface and carry negative charge, facilitating the dissociation of H2 to metal−H species (Hδ−) via homolytic cleavage of H2 similar to that occurring in metal ensembles. More importantly, the facile diffusion of Pt−H to the WOx support results in the formation of Brønsted acid sites (Hδ+), imparting bifunctionality to Pt1/WOx. The dynamic formation of Brønsted acid sites in hydrogen atmosphere proved to be the key to chemoselective hydrogenolysis of glycerol into 1,3-propanediol, which was experimentally demonstrated on the Pt1/WOx catalyst.

Controls on the formation of microbially induced sedimentary structures and biotic recovery in the Lower Triassic of Arctic Canada

Abstract Microbially induced sedimentary structures (MISS) are reportedly widespread in the Early Triassic and their occurrence is attributed to either the extinction of marine grazers (allowing mat preservation) during the Permo-Triassic mass extinction or the suppression of grazing due to harsh, oxygen-poor conditions in its aftermath. Here we report on the abundant occurrence of MISS in the Lower Triassic Blind Fiord Formation of the Sverdrup Basin, Arctic Canada. Sedimentological analysis shows that mid-shelf settings were dominated by deposition from cohesive sand-mud flows that produced heterolithic, rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks. The absence of storm beds and any other “event beds” points to an unusual climatic regime of humid, quiet conditions characterized by near continuous run off. Geochemical proxies for oxygenation (Mo/Al, Th/U, and pyrite framboid analysis) indicate that lower dysoxic conditions prevailed in the basin for much of the Early Triassic. The resultant lack of bioturbation allowed the development and preservation of MISS, including wrinkle structures and bubble textures. The microbial mats responsible for these structures are envisaged to have thrived, on sandy substrates, within the photic zone, in oxygen-poor conditions. The dysoxic history was punctuated by better-oxygenated phases, which coincide with the loss of MISS. Thus, Permo-Triassic boundary and Griesbachian mudrocks from the deepest-water settings have common benthos and a well-developed, tiered burrow profile dominated by Phycosiphon. The presence of the intense burrowing in the earliest Triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the Permian. The notion that Early Triassic MISS preservation was caused by the extinction of mat grazers is not tenable.

Oxygen adsorption on Graphene/GaN (0001) surface: A first-principles study

Graphene or reduced-graphene-oxide are used in gallium nitride-based electronic devices because of similar properties such as transparency and high thermal conductivity. To date, there is not a detailed theoretical discussion of the oxygen adsorption on Graphene/GaN (0001) surface in the Literature. In this study, using the Density Functional Theory, we investigate the changes in the interactions between carbon and gallium atoms caused by the adsorption of oxygen atoms on the 3√3 × 3√3 graphene/ 4 × 4 GaN(0001) surface. Based on analysis of Electron Localization Function we have determined that the presence of covalent bonds between carbon and gallium atoms, in the surface without oxygen adsorbed, that produced a vertical buckling in graphene of 0.54 Å and 0.22 Å in the topmost gallium layer. The adsorption of oxygen on the surface caused the increment of the vertical buckling on both values; In this case, with 11 oxygen atoms adsorbed, it increases up to 1.01 Å in graphene and 0.38 Å in the topmost gallium layer. This effect causes a reordering of carbon-gallium bonds and modifies its bond length. Furthermore, based on the obtained formation energies, when the surface is exposed to oxygen-poor conditions, it remains without oxygen atoms adsorbed; in contrast, when the surface is exposed to rich oxygen conditions, it favors the adsorption of oxygen starting from 7 atoms. After this point, to increase the oxygen adsorption on the surface is required to apply energy to the system.

Defect energetics of cubic hafnia from quantum Monte Carlo simulations

Cubic hafnia (${\mathrm{HfO}}_{2}$) is of great interest for a number of applications in electronics because of its high dielectric constant. However, common defects in such applications degrade the properties of hafina. We have investigated the electronic properties of oxygen vacancies and nitrogen substitution in cubic ${\mathrm{HfO}}_{2}$ using first-principles calculations based on density functional theory (DFT) and many-body diffusion Monte Carlo (DMC) methods. We investigate five different charge defect states of oxygen vacancies, as well as substitutional N defects which can lead to local magnetic moments. Both DMC and DFT calculations shows that an oxygen vacancy induces strong lattice relaxations around the defect. Finally, we compare defect formation energies, charge and spin densities obtained from DMC with results obtained using DFT. While the obtained formation energies from DMC are 0.6--1.5 eV larger than those from $\mathrm{GGA}+U$, the agreement for the most important defects, neutral and positively charged oxygen vacancies, and nitrogen substitutional defect, under oxygen-poor conditions are in reasonably good agreement. Our work confirms that nitrogen can act to passivate cubic hafnia for applications in electronics.

Polycyclic aromatic hydrocarbons (PAHs) in sediment cores from lakes Shinji and Nakaumi, SW Japan: A proxy of recent fire events in the watershed

PAHs in sediment cores have been investigated as a useful proxy of historic fire events in the watershed of an estuary. Oxygen poor and anoxic lake bottom conditions in estuarine brackish lakes Shinji and Nakaumi could prevent the oxidization of polycyclic aromatic hydrocarbons (PAHs) and preserve a record of PAHs in sediments. PAHs emitted from wood and/or grass burning have been analyzed for composition and concentrations during the last ∼300 years. Carbonized plant material which remained after artificial agricultural fires and heating experiments have been used to estimate fire temperature. The equation relating maximum temperature and hydrogen to carbon (H/C) atomic ratio of the charcoal is as follows: Temp (°C) = 317 x (H/C)−0.708 (R2 = 0.924, 200–700 °C).These experiments and the gas chromatography - mass spectrometry analysis of PAHs on the charcoals suggest that PAHs were primarily produced at temperatures less than 500 °C in the burning of wild plants.The PAHs contents in the two sediment cores were not related to total organic carbon (TOC) contents and emission of industrial waste, and were directly due to fire events in this region. Although TOC contents of the sediments were constant at about 0.5% in Lake Shinji and 1.0% in Lake Nakaumi before ca. 1900 CE, and increased up to about 4% due to recent nutrient discharge, the profiles of PAHs contents were completely different. The sediment cores contained the following PAHs: phenanthrene (P), fluoranthene (Fla), pyrene (Py), benz[a]anthracene (BaAn), benzofluoranthenes (Bflas), benzo[e]pyrene (BePy), indeno[1,2,3-cd]pyrene (InPy) and benzo[ghi]perylene (BghiP). The contents of 6-ring InPy and BghiP, high temperature markers, are lower than those of the other low ring Py, BaAn, Bflas and BePy, showing low to medium intensity/temperature fire events. Relatively higher BaAn contents suggest that the PAHs were carried and deposited in the sediments for a short period after the fire. The PAHs peak groups B (1830–1870 CE) and C (1920 CE) may be attributed to the burning of wood buildings in Matsue City, and the PAHs peak group period D (1970–1980 and 2000–2007 CE) could be mainly due to forest fires. The general increase in PAHs after 1850 CE could be caused by climate change after the Little Ice Age. The PAHs with maximum total peak concentrations at 30–34 cm depth (1850 CE: 4890 ng g−1) in Lake Shinji and at 8–12 cm depth (1970–1980 CE: 2030 ng g−1) in Lake Nakaumi are not at a toxic level.

Structural Evolution of α-Fe2O3(0001) Surfaces Under Reduction Conditions Monitored by Infrared Spectroscopy.

The precise determination of the surface structure of iron oxides (hematite and magnetite) is a vital prerequisite to understand their unique chemical and physical properties under different conditions. Here, the atomic structure evolution of the hematite (0001) surface under reducing conditions was tracked by polarization-resolved infrared reflection absorption spectroscopy (IRRAS) using carbon monoxide (CO) as a probe molecule. The frequency and intensity of the CO stretch vibration is extremely sensitive to the valence state and electronic environments of surface iron cations. Our comprehensive IRRAS results provide direct evidence that the monocrystalline, stoichiometric α-Fe2O3(0001) surface is single Fe-terminated. The initial reduction induced by annealing at elevated temperatures produces surface oxygen vacancies, where the excess electrons are localized at adjacent subsurface iron ions (5-fold coordinated). A massive surface restructuring occurs upon further reduction by exposing to atomic hydrogen followed by Ar+-sputtering and annealing under oxygen poor conditions. The restructured surface is identified as a Fe3O4(111)/Fe1−xO(111)-biphase exposing both, Fe3+ and Fe2+ surface species. Here the well-defined surface domains of Fe3O4(111) exhibit a Feoct2-termination, while the reduced Fe1−xO(111) is Fe2+(oct)-terminated. These findings are supported by reference IRRAS data acquired for CO adsorption on magnetite (111) and (001) monocrystalline surfaces.

How quick was marine recovery after the end-Triassic mass extinction and what role did anoxia play?

Oxygen restricted conditions were widespread in European shelf seas after the end-Triassic mass extinction event and they are reported to have hindered the recovery of marine benthos. Here we reconstruct the redox history of the Early Jurassic Blue Lias Formation of southwest Britain using pyrite framboid size analysis and compare this with the recovery of bivalves based on field and museum collections. Results suggest widespread dysoxia punctuated by periods of anoxia in the region, with the latter developing frequently in deeper water settings. Despite these harsh conditions, initial benthic recovery occurred rapidly in the British Jurassic, especially in shallowest settings, and shows no relationship with the intensity of dysoxia. A stable diversity was reached by the first recognised ammonite zone after the end-Triassic mass extinction. This contrasts with the deeper-water, more oxygen-poor sections where the diversity increase was still continuing in the earliest Sinemurian Stage, considerably longer than previously reported. Similar recovery rates are seen amongst other groups (brachiopods and ammonites). Oxygen-poor conditions have been suggested to delay recovery after the Permo-Triassic mass extinction, but this is not the case after the end-Triassic crisis. We suggest that this was because the European dysoxia was only a regional phenomenon and there were plenty of well-ventilated regions available to allow an untrammelled bounce back.

Paleoceanographic changes in the Northern East China Sea during the last 400 kyr as inferred from radiolarian assemblages (IODP Site U1429)

The East China Sea (ECS) is a shallow marginal sea that is sensitive to glacio-eustatic sea-level changes and is influenced by warm oligotrophic water of the Kuroshio Current (KC), the nutrient-rich Taiwan Warm Current, and freshwater discharges from rivers in southern China during the East Asian summer monsoon season. In this area, local paleoceanographic changes for times prior to 40 ka remain poorly studied because of high sediment accumulation rates on the seafloor. During Integrated Ocean Drilling Program Expedition 346, long sediment cores representing the last 400 kyr were retrieved from the northern part of the ECS (Site U1429). In these cores, radiolarians are abundant and well-preserved, thus using the ecological properties of radiolarians, we analyzed how glacio-eustatic sea-level variations have influenced the paleoceanography of the ECS over the last 400 kyr, with a focus on changes in water properties at intermediate depths. Additionally, the summer sea surface temperature (SST) and intermediate water temperature at about 500 m were quantified by means of data on selected radiolarian species. The KC influenced the shallow water at Site U1429 during each interglacial period over the last 400 kyr (marine isotope stages [MISs] 1, 5, 7, 9, and 11), causing a high summer SST (about 27 °C), although inflow of the KC into the ECS was probably delayed until after the sea-level maximum of interglacial MIS 1 and MIS 5. During this lag time, ECS shelf water was the dominant influence on the system. During glacial periods (MISs 2–4, 6, and 10), our data suggest that coastal conditions prevailed, probably because of a sea-level drop of more than 90 m. At these times, the summer SST was colder, ca. 20 °C. Changes in the relative abundance of Cycladophora davisiana indicate that the most significant changes in the bottom water occurred during MIS 6, when the bottom water likely became poorer in oxygen. An increase in the shallow-water primary productivity during MIS 7 and MIS 6 was probably the key factor causing the oxygen-poor conditions.

Petrologic and geochemical evidence for the formation of organic-rich siliceous rocks of the Late Permian Dalong Formation, Lower Yangtze region, southern China

Abstract Black shales are economically and scientifically important because they are commonly associated with high-quality hydrocarbon source rocks and metal accumulations formed during periods of abrupt environmental change. Organic-rich siliceous rocks of the Late Permian Dalong Formation developed extensively within Middle–Upper Yangtze region (western Yangtze platform); however, the formation mechanism of its formation in the Lower Yangtze region (eastern Yangtze platform) remains a subject of debate due to a lack of outcrop exposure. Petrologic, mineralogic, and geochemical data are presented for three sections of the Dalong Formation within the Lower Yangtze region. Geochemical ratios including V/(V + Ni), V/Cr, Ni/Co, U/Th, and V/Sc suggest that the Dalong Formation was deposited in an oxygen-poor environment. The elevated concentration of Mo (>100 ppm) further suggests that free H2S existed in the bottom water, which was favorable for the accumulation of large amounts of organic matter. Mo/TOC ratios reveal that water flow in the Lower Yangtze Basin was moderately to strongly restricted during deposition of the Dalong Formation. Flow within the upper–middle parts of the Yangtze Basin was also restricted, suggesting that northern marginal basins on the Yangtze Platform formed part of a single ocean during the Late Permian (i.e., Changhsingian). Cherts of the Dalong Formation reflect high primary productivity, similar to that of modern-day upwelling zones, which increased the amount of organic matter. These results, combined with previous work, suggest that the long-term oxygen-poor conditions during deposition of the Dalong Formation were caused by restricted water circulation in a unique paleogeographic environment characterized by low latitude and submarine paleo-highlands. Such settings of low latitude characterized by tropical climate favored the growth of siliceous zooplankton in the zones with submarine paleo-highlands having created topographic barriers to water circulation. Restricted bottom-water flow and oceanic anoxia during the Late Permian were likely the main controls on the accumulation of organic-rich rocks. Elevated nutrient levels caused by frequent oceanic upwelling along the western margin of the South China Craton and global volcanism at this time facilitated siliceous organism productivity.

Polarons, vacancies, vacancy associations, and defect states in multiferroic BiFeO3

Oxygen, bismuth, and iron vacancies are studied by density-functional theory calculations in multiferroic bismuth ferrite in oxidative and reducing external conditions. We accurately describe the localized electronic states associated with isolated defects. Oxygen-rich conditions provide fully ionized oxygen vacancies, and ionized or partially ionized cationic vacancies, possibly yielding $p$-type conductivity mediated by oxygen-type holes. Oxygen-poor conditions provide fully ionized vacancies and a much smaller concentration of electronic carriers. Cationic and oxygen vacancies tend to pair (Bi-O, Fe-O) with an associated electric dipole being as close as possible to the polar axis, possibly leading to imprint effects. This clustering also results in an extended stability domain for the ionized defects. Furthermore, O and Fe vacancies are respectively associated with Fe-$3d$ and O-$2p$ type moderately deep defect states spatially localized close to the defect. The charge-neutral Fe vacancy possesses an electric dipole, despite being a point defect. Bi vacancies may be found in several metastable electronic states, with in the most stable one, a mid-gap band of defect states with Fe-$3d$ character, in addition to the three O-$2p$ defect states associated to the acceptor nature of this defect. Finally, electrons released in the lattice by oxygen vacancies, if not captured by acceptor defects, tend to localize as small polarons, while holes released by cationic vacancies, if not captured by donor defects, are associated with delocalized Bloch-like band states.

Metallicity in SrTiO3 substrates induced by pulsed laser deposition

Oxygen deficiency has been known to induce metallic conduction in bulk and thin film SrTiO3 (STO). Here, we report on the metallicity of STO substrates induced by the pulsed laser deposition (PLD) process of STO films under various oxygen-poor growth conditions. Depositions as short as 2 min result in conduction through the STO substrate. Films grown on other substrates are insulating, and STO substrates annealed under the same growth conditions without laser ablation remain insulating. By varying background gas composition during deposition, we find that the transport behavior transitions from metallic to insulating behavior at progressively higher ambient pressures for O2, 99% N2/1% O2, N2, and Ar. Metallic behavior persists to deposition pressures as high as 10−2 Torr in Ar. These results suggest that, during the PLD process, the deposition kinetics and plume energy are a dominant factor in the formation of oxygen vacancies which then diffuse into the substrate. Understanding these mechanisms is crucial to prevent STO substrate reduction during PLD of films which require low O2 partial pressures during growth.

Testing laboratory parameters of compost tea

During the industrial production of broiler chicken, a large amount of manure is produced, of which easily contained nitrogen content (without pre-treatment) is released into the atmosphere as an air pollutant. In our experiments, we aimed to prepare compost tea, also known as water extract of compost, from pre-treated poultry manure in order to create a product can be utilized as liquid nutrient supply. The poultry manure source was the Baromfi-Coop Ltd. located in Nyírjákó, Hungary, where it was treated by composting. As a result of this pre-treatment of the poultry manure, its nutrient parameters improve and nitrogen is present in a form that is better utilized for plants. Furthermore, this product is suitable for further utilization and also can be the base material for a brand-new product. For this reason the effects of compost/water ratio, incubation time, low oxygen level, and extraction time on the parameters of the resulted product were studied in the frame of developing new soil-life enhancing microbial product, so-called compost tea.&#x0D; Chemical parameters of the compost used as base material strongly determined the properties of the resulted compost tea, especially the ratio of the various nitrogen forms, their concentration and the salt content. It was found that adding water at a higher rate that means 1/40 and 1/50 mixing ratios results in more cost-effective production. In the experiment the compost tea were held under oxygen-poor conditions, therefore pH of the extractions decreased, which influenced the quality and quantity of their nutrient content.

Effect of V-containing precursors on the structure and catalytic performance of Cs-substituted phosphomolybdates for isobutane oxidation

A series of vanadium-substituted Cs salt of heteropoly compounds (HPC) from different vanadium-containing precursors were synthesized to investigate the preferable vanadyl species for oxidation of isobutane to methacrylic acid (MAA) under oxygen-poor conditions. The effects of various precursors on the structure were explored by XRD, FT-IR, Raman, UV–vis diffuse reflectance, XPS, H2-TPR, NH3-TPD and IR spectra of pyridine adsorption, and their structure-performance relationship was further studied. It was firstly found that the vanadium-containing precursors played a crucial role in the structure (location of vanadyl species), surface acidity and redox properties (ratio of surface V4+/V5+ and Mo5+/Mo6+ redox couples) for series of as-prepared HPCs catalysts. The catalyst derived from vanadyl sulfate led to vanadyl species into the secondary structure of Keggin-type HPC, which exhibited suitable surface V4+/V5+ and Mo5+/Mo6+ ratio and higher surface acidity, thereby improving the catalytic activity and selectivity to MAA for selective oxidation of isobutane under oxygen-poor conditions. These understandings would be beneficial for further study of HPCs and developing of highly efficient catalysts for isobutane oxidation.

Trace element (Mn, Zn, Ni, V) and authigenic uranium (aU) geochemistry reveal sedimentary redox history on the Juan de Fuca Ridge, North Pacific Ocean

Changes in meridional overturning circulation and water mass chemistry can be recorded by oxygen concentrations in the deep ocean. Because the deep Pacific is the largest ocean reservoir, its oxygen concentrations may be related to global climate change. In this study, oxygen conditions in the past are reconstructed by contrasting the sedimentary geochemistry of multiple redox-sensitive trace elements (Mn, Ni, Zn, V corrected for terrigenous and hydrothermal inputs) and authigenic U (aU) from six sediment cores on the Juan de Fuca Ridge from 2.7-2.8 km depth. We find that Mn and Ni are indicators for oxygen-rich conditions, while Zn, V, and aU are indicators for oxygen-poor conditions. Relative Redox Potentials (RRPs) for each core are calculated by converting excess metal fluxes into binary presence/absence designations, weighting each element by the strength and direction of its redox indication, summing the five elements, and then averaging the data in 5kyr bins. Metal depositional histories from all six cores demonstrate low oxygen conditions during interglacial periods, particularly during 100–120 ka (MIS5) but also 200–250 ka (MIS7), and high oxygen conditions during glacial periods (MIS2-4 and MIS6). This redox pattern does not appear to be driven by organic matter flux to the sediment, as reconstructed by three different paleo-productivity proxies (organic carbon, opal, and excess barium). Instead higher oxygen concentrations on the Juan de Fuca Ridge may be a result of better ventilation during glacial periods, possibly due to enhanced North Pacific Intermediate Water formation. Alternatively, sedimentary redox conditions on the Juan de Fuca Ridge may be locally controlled by the deposition of hydrothermal sulfides from nearby vent fields.

Ab Initio Study on Surface Segregation and Anisotropy of Ni-Rich LiNi1–2yCoyMnyO2 (NCM) (y ≤ 0.1) Cathodes

Advances in ex situ and in situ (operando) characteristic techniques have unraveled unprecedented atomic details in the electrochemical reaction of Li-ion batteries. To bridge the gap between emerging evidences and practical material development, an elaborate understanding on the electrochemical properties of cathode materials on the atomic scale is urgently needed. In this work, we perform comprehensive first-principle calculations within the density functional theory + U framework on the surface stability, morphology, and elastic anisotropy of Ni-rich LiNi1-2yCoyMnyO2 (NCM) (y ≤ 0.1) cathode materials, which are strongly related to the emerging evidence in the degradation of Li-ion batteries. On the basis of the surface stability results, the equilibrium particle morphology is obtained, which is mainly determined by the oxygen chemical potential. Ni-rich NCM particles are terminated mostly by the (012) and (001) surfaces for oxygen-poor conditions, whereas the termination corresponds to the (104) and (001) surfaces for oxygen-rich conditions. Besides, Ni surface segregation predominantly occurs on the (100), (110), and (104) nonpolar surfaces, showing a tendency to form a rocksalt NiO domain on the surface because of severe Li-Ni exchange. The observed elastic anisotropy reveals that an uneven deformation is more likely to be formed in the particles synthesized under poor-oxygen conditions, leading to crack generation and propagation. Our findings provide a deep understanding of the surface properties and degradation of Ni-rich NCM particles, thereby proposing possible solution mechanisms to the factors affecting degradation, such as synthesis conditions, coating, or novel nanostructures.