Gas-phase Oxygen Research Articles

The OTELO survey

Context. A sample of low-mass Hα emission line sources at z ∼ 0.4 was studied in the context of the mass-metallicty relation (MZR) and its possible evolution. We drew our sample from the OSIRIS Tunable Emission Line Object (OTELO) survey, which exploits the red tunable filter of OSIRIS at the Gran Telescopio Canarias to perform a blind narrow-band spectral scan in a selected field of the Extended Groth Strip. We were able to directly measure emission line fluxes and equivalent widths from the analysis of OTELO pseudo-spectra. Aims. This study aims to explore the MZR in the very low-mass regime. Our sample reaches stellar masses (M*) as low as 106.8 M⊙, where 63% of the sample have M* < 109 M⊙. We also explore the relation of the star formation rate (SFR) and specific SFR with M* and gas-phase oxygen abundances, as well as the M*-size relation and the morphological classification. Methods. The M* were estimated using synthetic rest-frame colours. Using an χ2 minimization method, we separated the contribution of [N II]λ6583 to the Hα emission lines. Using the N2 index, we separated active galactic nuclei from star-forming galaxies (SFGs) and estimated the gas metallicity. We studied the morphology of the sampled galaxies qualitatively (visually) and quantitatively (automatically) using high-resolution data from the Hubble Space Telescope-ACS. The physical size of the galaxies was derived from the morphological analysis using GALAPAGOS2/GALFIT, where we fit a single-Sérsic 2D model to each source. Results. We find no evidence for an MZR evolution from comparing our very low-mass sample with local SFGs from the Sloan Digital Sky Survey. Furthermore, the same is true for M*-size and M*-SFR relations, as we deduce from comparison with recent literature. Morphologically, our sample is mostly (63%) populated by late-type galaxies, with 13% of early-type sources. For the first time, we identify one possible candidate outlier in the MZR at z = 0.4. The stellar-mass, metallicity, colour, morphology, and SFR of this source suggest that it is compatible with a transitional dwarf galaxy.

The Leoncino Dwarf Galaxy: Exploring the Low-metallicity End of the Luminosity–Metallicity and Mass–Metallicity Relations*

Abstract Extremely metal-poor (XMP) galaxies are low-mass, star-forming galaxies with gas-phase oxygen abundances below 12 + log(O/H) = 7.35 ( Z ). Galaxy evolution scenarios suggest three pathways to form an XMP: (1) secular evolution at low galaxy masses, (2) slow evolution in voids, or (3) dilution of measured abundances from infall of pristine gas. The recently discovered XMP galaxy Leoncino, with an oxygen abundance below 3% Z , provides an opportunity to explore these different scenarios. Using Hubble Space Telescope imaging of the resolved stellar populations of Leoncino, we measure the distance to the galaxy to be Mpc and find that Leoncino is located in an underdense environment. Leoncino has a compact morphology, hosts a population of young, massive stars, has a high gas-to-star mass ratio, and shows signs of interaction with a galaxy nearby on the sky, UGC 5186. Similar to nearly all XMP galaxies known in the nearby universe, Leoncino is offset from the Luminosity–Metallicity (LZ) relation. However, Leoncino is consistent with the stellar Mass–Metallicity (MZ) relation defined by Local Volume galaxies. Thus, our results suggest that the offset from the LZ relation is due to higher recent star formation, likely triggered by a minor interaction, while the low oxygen abundance is consistent with the expectation that low-mass galaxies will undergo secular evolution marked by inefficient star formation and metal loss via galactic winds. This is in contrast to XMP galaxies that are outliers in both the LZ and MZ relations; in such cases, the low oxygen abundances are best explained by dilution due to the infall of pristine gas. We also discuss why quiescent XMP galaxies are underrepresented in current surveys.

Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co3O4 hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal-organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths-namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites-were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = -1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co3O4, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic performance in toluene oxidation, it achieved a toluene conversion of 90% (T90) at ∼227 °C (a space velocity of 60 000 mL g-1 h-1) and the activity energy (Ea) is 69.5 kJ mol-1. A series of characterizations were performed to investigate the structure-activity correlation. It was found that there are more structure defects, more adsorbed surface oxygen species, more surface Co3+ species, and higher reducibility at low temperatures on the Co-MeCN-O than on other Co3O4 samples; these factors are responsible for its excellent catalytic performance. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that, when there is no oxygen in the atmosphere, the lattice oxygen may be involved in the activation of toluene, and the gas-phase oxygen replenished by the oxygen vacancies was essential for the total oxidation of toluene on the surface of the Co-MeCN-O catalysts, it also proves the importance of oxygen vacancies. Moreover, for the Co-MeCN-O catalysts, no obvious decrease in catalytic performance was observed after 120 h at 220 °C and it is still stable after cycling tests, which indicates that it exhibits excellent stability for toluene oxidation. This study sheds lights on the controllable synthesis of macroporous-microporous materials in single-crystalline form without an external template, and, thus, it may serve as a reference for future design and synthesis of hollow porous materials with outstanding catalytic performance.

Present-day mass-metallicity relation for galaxies using a new electron temperature method

Aims.We investigate electron temperature (Te) and gas-phase oxygen abundance (ZTe) measurements for galaxies in the local Universe (z < 0.25). Our sample comprises spectra from a total of 264 emission-line systems, ranging from individual HIIregions to whole galaxies, including 23 composite HIIregions from star-forming main sequence galaxies in the MaNGA survey.Methods.We utilise 130 of these systems with directly measurableTe(OII) to calibrate a new metallicity-dependentTe(OIII)–Te(OII) relation that provides a better representation of our varied dataset than existing relations from the literature. We also provide an alternativeTe(OIII)–Te(NII) calibration. This newTemethod is then used to obtain accurateZTeestimates and form the mass – metallicity relation (MZR) for a sample of 118 local galaxies.Results.We find that all theTe(OIII)–Te(OII) relations considered here systematically under-estimateZTefor low-ionisation systems by up to 0.6 dex. We determine that this is due to such systems having an intrinsically higher O+abundance than O++abundance, renderingZTeestimates based only on [OIII] lines inaccurate. We therefore provide an empirical correction based on strong emission lines to account for this bias when using our newTe(OIII)–Te(OIII) andTe(OIII)–Te(NII) relations. This allows for accurate metallicities (1σ = 0.08 dex) to be derived for any low-redshift system with an [OIII]λ4363 detection, regardless of its physical size or ionisation state. The MZR formed from our dataset is in very good agreement with those formed from direct measurements of metal recombination lines and blue supergiant absorption lines, in contrast to most otherTe-based and strong-line-based MZRs. Our newTemethod therefore provides an accurate and precise way of obtainingZTefor a large and diverse range of star-forming systems in the local Universe.

High sensitive gas sensor based on vertical graphene field effect transistor

A gas sensor made from graphene vertical field effect transistor (VGr-FET) has been fabricated using graphene as the source electrode, C60 thin film as the semiconductor layer and aluminum thin film as the drain electrode. The on/off ratio of transistor gated by bottom electrode with ionic liquid gel as dielectric layer is derived to be 103 from measured source–drain current Ids. The apparent energy barrier height between the graphene and polycrystalline fullerene was calculated from the model of heterojunction diode I–V response curves. The barrier height φBH was altered by the gating potential vertically applied on graphene sheet, resulting the large on/off ratio of the transistor. The effect of surface adsorption of water vapor, oxygen, ammonia and isoprene gas phase molecules on the Ids was measured. The lower limit of detection (LOD) for ammonia (86 ppb) than that of isoprene (420 ppb) is attributed to the donor nature of ammonia contact with p-type graphene, and the adsorbed donor leads to a corresponding positive gating effect to the VGr-FET. This facile, low cost and quick responsive device shows promise for early diagnose of severe human respiratory diseases.

The Multi-object Spectroscopy Observation of Seven Interacting Galaxy Pairs: Metallicity Gradients and Star Formation Distributions

We use the Multi-Object Spectroscopy system of Xinglong 2.16 m telescope to study the gradients of gas-phase oxygen abundance and the distributions of star formation activities of seven nearby interacting galaxy pairs. On the basis of emission line luminosities and flux ratios, we estimate the gas-phase metallicities (log(O/H)), excitation mechanisms, and star formation rates (SFRs) of different regions in each galaxy. The average radial slope of log(O/H) from linear fitting of galaxy pairs in our sample is significantly flatter than that of isolated disk galaxies, also the central metallicity is much lower for interacting galaxies. This supports the predictions and results of previous theoretical numerical simulations and observational works which show the cold gas inflows induced by galaxy interactions can dilute the central metallicity. From the analysis of the radial distribution of SFR surface densities (ΣSFR), we find that, in our sample, galaxies in Spiral–Spiral (S+S) pairs have peak ΣSFR at the center region and lower SFRs at the outer parts than that at the center. On the other hand, for two spirals in Spiral-Elliptical (S+E) pairs (Arp142 and J0338+2120), they both have relatively higher (ΣSFR) in their off-nuclei regions. This may hint a dependence of star formation distributions for paired galaxies on their companion morphologies.

Sucrose-Assisted Solution Combustion Synthesis of Doped Strontium Ferrate Perovskite-Type Electrocatalysts: Primary Role of the Secondary Fuel

The methodologies and experimental conditions used for the synthesis of cathode materials for electrochemical devices strongly influence their electrocatalytic performance. In particular, solution combustion synthesis is a convenient and versatile methodology allowing a fine-tuning of the properties of the material. In this work, we used for the first time a sucrose assisted-solution combustion synthesis for the preparation of Cerium and Cobalt-doped SrFeO3–δ electrocatalysts and we investigated the effect of polyethylene glycol (PEG) addition as a secondary fuel on their structural, microstructural, redox and electrochemical properties. The perovskite-type powders were characterized by X-ray diffraction coupled with Rietveld refinement, scanning, and high-resolution transmission electron microscopies, thermogravimetric analysis, nitrogen adsorption measurements, and temperature-programmed reduction. Electrical conductivity and overpotential measurements were performed after the deposition of the powders onto a Gd-doped ceria electrolyte pellet. Stable high-valence B-site cations were detected in the powders prepared from sucrose-PEG fuel mixtures, although a substantial improvement of the conductivity and a decrease of the overpotential values were obtained only with high molecular weight PEG. The superior electrochemical performance obtained using PEG with high molecular weight has been ascribed to a faster interaction of the powder with the oxygen gas phase favored by the nanometer-sized crystalline domains.

Reactive metallocene cations as sensitive indicators of gas-phase oxygen and water.

Analysis of highly reactive compounds at very low concentration in solution using electrospray ionization mass spectrometry requires the use of exhaustively purified solvents. It has generally been assumed that desolvation gas purity needs to be similarly high, and so most chemists working in this space have relied upon high purity gas. However, the increasing competitiveness of nitrogen generators, which provide gas purity levels that vary inversely with flow rate, prompted an investigation of the effect of gas-phase oxygen on the speciation of ions. The most reactive species studied, the reduced titanium complex [Cp2Ti(NCMe)2]+[ZnCl3]- and the olefin polymerization pre-catalyst [Cp2Zr(μ-Me)2AlMe2]+[B(C6F5)4]-, only exhibited detectable oxidation when they were rendered coordinatively unsaturated through in-source fragmentation. Computational chemistry allowed us to find the most plausible pathways for the observed chemistry in the absence of observed intermediates. The results provide insight into the gas-phase oxidation or hydrolysis of these reactive species.

Gradual adaptation of facultative anaerobic pathogens to microaerobic and anaerobic conditions.

Many notable human pathogens are facultative anaerobes. These pathogens exhibit redundant metabolic pathways and a whole array of regulatory systems to adapt to changing oxygen levels. However, our knowledge of facultative anaerobic pathogens is mostly based on fully aerobic or anaerobic cultures, which does not reflect real infection conditions, while the microaerobic range remains understudied. Here, we examine the behavior of pathogenic and nonpathogenic strains of two facultative anaerobes, Escherichia coli and Pseudomonas aeruginosa, during the aerobic-anaerobic transition. To do so, we introduce a new technique named AnaeroTrans, in which we allow self-consumption of oxygen by steady-state cultures and monitor the system by measuring the gas-phase oxygen concentration. We explore the different behavior of the studied species toward oxygen and examine how this behavior is associated with the targeted infection sites. As a model, we characterize the adaptation profile of the ribonucleotide reductase network, a complex oxygen-dependent enzymatic system responsible for the generation of the deoxyribonucleotides. We also explore the actions of the most important anaerobic regulators and how these regulators influence bacterial fitness. Our results allow us to classify the different elements that compose the aerobic-anaerobic transition into reproducible stages, thus showing the different adaptation mechanisms of the studied species.

Characterization of Oxygenaceous Species Formed by Exposure of Ag(111) to Atomic Oxygen

The uptake and chemical speciation of oxygen in and on Ag(111) surface is described. An Ag(111) surface was exposed to gas-phase oxygen atoms under ultrahigh vacuum compatible conditions at various surface temperatures. The O uptake was quantified using temperature-programmed desorption measurements and showed that oxygen exposures at temperatures above 500 K yielded only surface-adsorbed oxygen in a single surface reconstruction. At temperatures below 500 K, O uptake continued past O surface saturation, and a maximum in the uptake with respect to exposure temperature was observed at 450 K. A model where O atoms must diffuse out of subsurface absorption sites to free room for further O describes this observation. The chemical speciation of the oxygenaceous species formed under these conditions was achieved using X-ray photoelectron spectroscopy. These data show that a single O species initially formed on the surface, but at higher coverages, a new, three-dimensional oxygenaceous phase developed. Because of the importance of silver in heterogeneously catalyzed partial oxidation reactions, these results show that oxygen species embedded below the surface plane must be incorporated into accurate models of Ag-surface catalyzed reactions.

Mapping Metallicity Variations across Nearby Galaxy Disks

Abstract The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 H ii regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) optical integral field spectroscopy as part of the PHANGS–MUSE survey. After removing the first-order radial gradients present in each galaxy, we look at the statistics of the metallicity offset (ΔO/H) and explore azimuthal variations. Across each galaxy, we find low (σ = 0.03–0.05 dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those H ii regions that are 1σ outliers toward both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher Hα luminosity, lower Hα velocity dispersion, younger star clusters, and associated molecular gas clouds showing higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased Hα velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but cannot always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the interstellar medium.

Star formation and gas flow history of a dwarf irregular galaxy traced by gas-phase and stellar metallicities

ABSTRACT Studying the evolution of dwarf galaxies can provide insights into the characteristics of systems that can act as building blocks of massive galaxies. This paper discusses the history of star formation and gas flows (inflow and outflow) of a dwarf irregular galaxy in the Local Group, NGC 6822, from the viewpoint of gas-phase and stellar chemical abundance. Gas-phase oxygen abundance, stellar metallicity distribution, and gas fraction data are compared to chemical evolution models in which continuous star formation and gas flows are assumed. If the galaxy is assumed to be a closed or an accretion-dominated system where steeper stellar initial mass functions are allowed, the observed gas-phase oxygen abundance and gas fraction can be explained simultaneously; however, metallicity distributions predicted by the models seem to be inconsistent with the observed distribution, which suggests that the star formation, gas flows, and/or chemical enrichment are more complex than assumed by the models. When NGC 6822 is assumed to be a system dominated by outflow, the observed values of gas-phase oxygen abundance and gas fraction can be explained, and the metallicity distributions predicted by some of the models are also roughly consistent with the observed distribution in the metallicity range of −2.0 ≲ [Fe/H] ≲ −0.5. It should be noted that this result does not necessarily mean that the accretion of gas is completely ruled out. More observables, such as chemical abundance ratios, and detailed modelling may provide deeper insight into the evolution of the system.

Facet‐Dependent Activity of Co3O4 Catalyst for C3H8 Combustion

AbstractClarifying the facet‐dependent activity of Co3O4 towards C3H8 combustion is of great importance to have a deep understanding of reaction mechanism and develop highly active Co3O4 based catalysts for light hydrocarbon combustion. In this work, four different Co3O4 nanocatalysts which dominantly exposed {100}, {111}, {110} and {112} facets, respectively, were synthesized via hydrothermal method and further tested in C3H8 combustion. The catalytic activity of different crystal planes varied as the order of {111}>{100}>{110}>{112}. The Co3O4 catalyst with {111} facets exhibited the best catalytic performance with T50 and T90 as low as 209 and 239 °C, respectively. DRIFT and DFT calculations revealed that the facile activation of C−H bond on Co3O4 {111} planes is responsible for the high activity. Moreover, the higher activity of lattice oxygens and easy activation of gas phase oxygen could also contribute to the excellent catalytic performance.

Influence of strontium content on the oxygen surface exchange kinetics and oxygen diffusion in La1–xSrxCoO3–δ oxides

Oxygen surface exchange kinetics between the gas phase oxygen and La1–xSrxCoO3–δ (x = 0, 0.3, 0.4, 0.6) oxides at 0.67 kPa oxygen pressure in the 600–850°°С range were investigated. The mechanism within the two-step model including two consecutive stages, oxygen dissociative adsorption and oxygen adatom incorporation into the oxide lattice, was analysed. The oxygen diffusion coefficient (D), the rate of heterogeneous oxygen exchange (rH) and the elementary rates of this process — dissociative adsorption (ra) and incorporation (ri) — were determined. The effect of oxygen vacancy concentration, strontium segregation on the surface, temperature and oxygen pressure on rH, ra and ri are discussed.

Inerting effects of ammonium polyphosphate on explosion characteristics of polypropylene dust

This study experimentally investigated that the inerting effect of Ammonium Polyphosphate (APP) on characteristics of Polypropylene (PP) dust explosion. The results indicated that the maximum explosion pressure (Pmax), the explosion index (Kst) and the minimum explosion concentration (MEC) of PP powders were 8bar, 257barm/s and 25g/m3, respectively. Moreover, the minimum ignition energy (MIE) and the minimum ignition temperature (MIT) were 10mJ and 335°C, correspondingly for PP dust cloud. The explosion of PP powders could be inerted completely by 80wt% APP. In addition, the MIE of PP powders increased when the mass fraction of APP increased. Furthermore, APP had a significant inerting effect on the MIT of PP dust cloud. The MIT of PP powders increased by 80°C when the mass fraction of APP increased to 80wt %.Thermal analysis results showed that the introduction of APP could improve the thermal stability of PP. Furthermore, thermogravimetric analysis/infrared (TG-IR) spectroscopy was employed to gain insights into the pyrolysis mechanism of the PP/APP mixtures. The TG-IR results showed that the volatilized products formed in the pyrolysis were H2O and NH3 which could dilute and consume oxygen in gas phase.

The local properties of supernova explosions and their host galaxies

We aim to understand the properties at the locations of supernova (SN) explosions in their host galaxies and compare with the global properties of these host galaxies. We use the integral field spectrograph (IFS) of Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) to generate 2D maps of the parameter properties for 11 SN host galaxies. The sample galaxies are analyzed one by one in detail in terms of their properties of velocity field, star formation rate, oxygen abundance, stellar mass, etc. This sample of SN host galaxies has redshifts around , which is higher than those of previous related works. The higher redshift distribution allows us to obtain the properties of more distant SN host galaxies. Metallicity (gas-phase oxygen abundance) estimated from integrated spectra can represent the local metallicity at SN explosion sites with small bias. All the host galaxies in our sample are metal-rich galaxies (12+(O/H)) except for NGC 6387, which means SNe may be more inclined to explode in metallicity-rich galaxies. There is a positive relation between global gas-phase oxygen abundance and the stellar mass of host galaxies. We also try to compare the differences of the host galaxies between SNe Ia and SNe II. In our sample, both SNe Ia and SNe II can explode in normal galaxies, but SNe II can also explode in an interacting or a merging system, in which star formation is occurring in the galaxy.

The abundance and physical properties of O vii and O viii X-ray absorption systems in the EAGLE simulations

Abstract We use the EAGLE cosmological, hydrodynamical simulations to predict the column density and equivalent width distributions of intergalactic O vii ($E=574 \, \rm {eV}$) and O viii ($E=654 \, \rm {eV}$) absorbers at low redshift. These two ions are predicted to account for $40 \, \hbox{ per cent}$ of the gas-phase oxygen, which implies that they are key tracers of cosmic metals. We find that their column density distributions evolve little at observable column densities from redshift 1 to 0, and that they are sensitive to active galactic nucleus feedback, which strongly reduces the number of strong (column density $N \gtrsim 10^{16} \, \rm {cm}^{-2}$) absorbers. The distributions have a break at $N \sim 10^{16}\, \rm {cm}^{-2}$, corresponding to overdensities of ∼102, likely caused by the transition from sheet/filament to halo gas. Absorption systems with $N \gtrsim 10^{16} \, \rm {cm}^{-2}$ are dominated by collisionally ionized O vii and O viii, while the ionization state of oxygen at lower column densities is also influenced by photoionization. At these high column densities, O vii and O viii arising in the same structures probe systematically different gas temperatures, meaning their line ratio does not translate into a simple estimate of temperature. While O vii and O viii column densities and covering fractions correlate poorly with the H i column density at ${N}_{\rm {H}\, \rm {I}} \gtrsim 10^{15} \, \rm {cm}^{-2}$, O vii and O viii column densities are higher in this regime than at the more common, lower H i column densities. The column densities of O vi and especially Ne viii, which have strong absorption lines in the UV, are good predictors of the strengths of O vii and O viii absorption and can hence aid in the detection of the X-ray lines.

Interaction of H2O, O2 and H2 with Proton Conducting Oxides Based on Lanthanum Scandates

The research uses the method of high-temperature thermogravimetric analysis to study the processes of interaction of the gas phase in the temperature range 300–950 °C in the partial pressure ranges of oxygen 8.1–50.7 kPa, water 6.1–24.3 kPa and hydrogen 4.1 kPa with La1–xSrxScO3–α oxides (x = 0; 0.04; 0.09). In the case of an increase in the partial pressure of water vapor at a constant partial pressure of oxygen (or hydrogen) in the gas phase, the apparent level of saturation of protons is shown to increase. An increase in the apparent level of saturation of protons of the sample also occurs with an increase in the partial pressure of oxygen at a constant partial pressure of water vapor in the gas phase. The paper discusses the causes of the observed processes. The research uses the hydrogen isotope exchange method with the equilibration of the isotope composition of the gas phase to study the incorporation of hydrogen into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates. The concentrations of protons and deuterons were determined in the temperature range of 300–800 °C and a hydrogen pressure of 0.2 kPa for La0.91Sr0.09ScO3–α oxide. The paper discusses the role of oxygen vacancies in the process of incorporation of protons and deuterons from the atmosphere of molecular hydrogen into the structure of the proton conducting oxides La1–xSrxScO3–α (x = 0; 0.04; 0.09). The proton magnetic resonance method was used to study the local structure in the temperature range 23–110 °C at a rotation speed of 10 kHz (MAS) for La0.96Sr0.04ScO3–α oxide after thermogravimetric measurements in an atmosphere containing water vapor, and after exposures in molecular hydrogen atmosphere. The existence of proton defects incorporated into the volume of the investigated proton oxide from both the atmosphere containing water and the atmosphere containing molecular hydrogen is unambiguously shown. The paper considers the effect of the contributions of the volume and surface of La0.96Sr0.04ScO3–α oxide on the shape of the proton magnetic resonance spectra.

Unraveling Oxygen Evolution in Li-Rich Oxides: A Unified Modeling of the Intermediate Peroxo/Superoxo-like Dimers.

Peroxo/superoxo is a key intermediate in oxygen evolution/reduction reactions in (electro)catalysis. However, peroxo/superoxo analogues have aroused controversies relevant to the origin of oxygen-anion redox. Specifically, some characteristics such as the magnitude of the O-O bond length in bulk materials have been puzzling during oxygen oxidation, as has the relationship between the peroxo/superoxo intermediate and the release of oxygen. The latter is a major safety concern to the application of oxygen-anion redox in lithium ion batteries. Herein, we present a unified modeling of the full delithiation process for model system Li2MnO3 by using first-principles calculations. We find that the cationic antisite defects and the electron deficiency are two major limiting factors in the anionic oxidation whose state can evolve, as the degree of delithiation increases, from the electron/hole, through peroxo-like O2δ- dimer formation, to the eventual release of gas-phase oxygen molecule. During the delithiation process, the dangling oxygen (i.e., singly coordinated with Mn) pairs play a critical role in intermediate dimer formation. Meanwhile, we identify five generic binding patterns of O2δ- dimers with Mn ions for which the O-O bond length varies from 1.45 Å in the peroxo state to 1.22 Å in the gas-phase oxygen molecule. Moreover, the dominant features of the three molecular orbitals, σc, πa, and πb, are distinguished, with the corresponding energy levels being highly delocalized and mixed as a result of the interplay with the host lattice. This work provides a deep understanding of the intermediate states of the anionic redox and suggests new strategies that mitigate oxygen release for the design of highly efficient and safe Li-rich cathode materials.

Local analogs of high-redshift galaxies: Metallicity calibrations at high-redshift

AbstractWe study the metallicity calibrations in high-redshift galaxies using a sample of local analogs of high-redshift galaxies selected from the SDSS survey. Located in the same region on the BPT diagram as star-forming galaxies at z ∼ 2, these high-redshift analogs share the same ionized ISM conditions as high-redshift galaxies. We establish empirical metallicity calibrations between the direct gas-phase oxygen abundances and varieties of metallicity indicators in our local analogs using direct Te method. These new metallicity calibrations are the best means to measure the metallicity in high-redshift galaxies. There exist significant offsets between these new high-redshift metallicity calibrations and local calibrations. Such offsets are mainly driven by the evolution of the ionized ISM conditions from high-z to low-z.