Ambient Oxygen Partial Pressure Research Articles

Influence of the warped scale on the internal oxidation of hot-rolled Si-Mn high-strength steels

As a lightweight material with excellent performance, high-strength steel is of great importance in achieving lightweight, safety, and energy efficiency in automobile body construction. However, the occurrence of internal oxidation following hot-rolled coils can adversely affect the surface quality of the product. In this investigation, our focus centered on exploring the influence of warped scale on internal oxidation in hot-rolled coils (IOHC). The findings suggest that the decomposition of the warped scale seriously affects the IOHC behavior. Pure Fe particles appear preferentially at the location of the warped scale front, and the depth of internal oxidation is much greater than that at the location of the normal oxide scale. In addition, it is found that IOHC is controlled by the ambient oxygen partial pressure, and the rate of the phase transition of the oxide scale increased dramatically as the ambient oxygen partial pressure decreased. Additionally, the interface region between the warped scale and the substrate is meticulously characterized through the utilization of FIB/TEM techniques, enabling a comprehensive understanding of the structure and composition of the oxide at the interface.

A comparison of the effect of oxygen partial pressure on microstructural evolution of PAN fibers during industrial carbon fiber production line at different altitudes

Understanding and regulating the oxidative stabilization behavior of polyacrylonitrile (PAN) precursor fibers are critical subjects of high-performance carbon fiber production technologies. Here, we performed continuous stabilization and carbonization of PAN fibers at industrial carbon fiber production lines in different locales (different oxygen partial pressure in atmosphere), and investigated the microstructural evolution of the fibers with a systematically analysis at different stages. Influence of oxygen partial pressure in oxidative stabilization atmosphere on tensile modulus of the obtained carbon fibers was obvious. Oxygen diffused into PAN fibers during oxidative stabilization, more homogeneous and crosslinked structures generated under higher oxygen partial pressure atmosphere, and gave the stabilized fibers lower skin-core ratio. The graphite layers gradually generated in the subsequent carbonization stages, and the gathered graphite layers transformed into graphite microcrystalline, the wide-angle x-ray diffraction (WAXD) demonstrated that higher oxygen partial pressure conditions contributed to the generation of higher crystallite preferred orientation and bigger crystallite size, Raman spectroscopy also confirmed the obtained carbon fibers with higher oxygen partial pressure conditions possessed more ordered graphite structures. Thus, relatively higher oxygen partial pressure in air gave the stabilized fibers more crosslinked structures, and contributed to the formation of high-performance carbon fibers.

Electrical properties and redox stability of series novel high-entropy Bi2VO5.5-based oxides

Exceptional high ionic conductivities have been well documented in the Bi2VO5.5-based materials. However, the poor phase and redox stabilities under a reducing atmosphere hindered their wide applications. Herein, with the aim to improve the phase and redox stabilities under a reducing atmosphere, a high-entropy strategy of multiple-metal-doping was applied to prepare series Bi2V1–4x(GaSiTaZr)xO5.5-δ (0 ≤ x ≤ 0.1) materials by a traditional solid state reaction method. The results revealed that multiple-metal-doping could stabilize the tetragonal phase of Bi2VO5.5 to room temperature and shown good phase and structural stabilities under inert or high oxygen partial pressure atmospheres, as well as pure oxide ion conduction which was about two orders of magnitude higher than that of the parent material, e.g. ∼2.0×10−2 S/cm at 400 ºC for the x = 0.05 sample while ∼1.5×10−4 S/cm for the x = 0 sample. Although the Bi2V1–4x(CuNiNbTi)xO5.5-δ materials would still be readily reduced under a reducing environment and introduce strong electronic conduction, the phase stability was apparently improved. Thus, improving the redox stability and suppressing the electronic conduction of the stabilized Bi2VO5.5-based materials under a reducing atmosphere is still the direction we should strive for.

Deletion of both anaerobic regulator genes fnr and narL compromises the colonization of Salmonella Typhimurium in mice model.

Salmonella Typhimurium (STM), a zoonotic pathogen, can adjust its metabolic pathway according to the variations in the partial pressure of atmospheric oxygen and nitrate via fumarate nitrate reductase regulator (Fnr) and NarL, the response regulator for nitrate reductase. Both Fnr and NarL have been individually reported to be the contributors of virulent phenotypes of STM. Hypoxia along with nitrate-rich environment are prevalent in macrophages and the Salmonella-induced inflammatory lumen of the host's large intestine activates both fnr and narL genes. In this study, the double (fnr and narL) knockout STM showed a synergistic reduction in the swimming (62%), swarming (84%) and biofilm density (86%) phenotypes anaerobically in association with its significant aerobic attenuation. The intracellular replication of the double mutant was reduced by 2.3 logs in chicken monocyte-derived macrophages. Furthermore, the competitive index of the double mutant in liver and spleen was found to be 0.3 and 0.44 respectively at 120h post-infection (PI) in mice. Surprisingly, no double mutant could be recovered from the infected mouse liver 3 days PI. Histopathological findings showed moderate infiltration of mononuclear cells in the large intestine of mice infected with double mutant, but severe infiltration was seen with the wild-type strain.

Role of oxidation in thermal fatigue damage mechanisms and life of X38CrMoV5 (AISI H11) hot work tool steel

Hot work tools steels, which are submitted to severe solicitations in service, are often damaged by thermal fatigue and corrosion. Interrupted Thermal Fatigue experiments were performed on X38CrMoV5 tool steel between 100 and 650 °C, in air and reduced oxygen partial pressure atmospheres after primary or secondary vacuum. A thermal and thermo-mechanical analysis by finite element method was carried out to estimate the strains and stresses undergone by the axisymmetric disc-shaped specimen during thermal cycling. The morphology, structure and phase composition of the oxide layer were analysed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It was shown that the thickness, homogeneity, structure, and compacity of the oxide multilayer formed on the specimen changed depending on test atmosphere. In air, crack initiation and propagation were strongly assisted by oxidation, leading to reduced fatigue life compared to inert atmospheres. Steel softening was highlighted in sub-surface, whatever the test atmosphere.

In-situ synchrotron x-ray photoelectron spectroscopy study of medium-temperature baking of niobium for SRF application

In order to determine optimal parameters of vacuum thermal processing of superconducting radiofrequency niobium cavities exhaustive information on the initial chemical state of niobium and its modification upon a vacuum heat treatment is required. In the present work the chemical composition of the niobium surface upon ultra-high vacuum baking at 200 ∘C–400 ∘C similar to ‘medium-temperature baking’ and ‘furnace baking’ of cavities is explored in-situ by synchrotron x-ray photoelectron spectroscopy (XPS). Our findings imply that below the critical thickness of the Nb2O5 layer ( ≈1nm ) niobium starts to interact actively with surface impurities, such as carbon and phosphorus. By studying the kinetics of the native oxide reduction, the activation energy and the rate-constant relation have been determined and used for the calculation of the oxygen-concentration depth profiles. It has been established that the controlled diffusion of oxygen is realized at temperatures 200 ∘C–300 ∘C, and the native-oxide layer represents an oxygen source, while at 400 ∘C the pentoxide is completely reduced and the doping level is determined by an ambient oxygen partial pressure. Fluorine (F to Nb atomic ratio is 0.2) after the buffered chemical polishing was found to be incorporated into the surface layer probed by XPS ( ≈4.6nm ), and its concentration increased during the low-temperature baking (F/Nb = 0.35 at 230 ∘C) and depleted at higher temperatures (F/Nb = 0.11 at 400 ∘C). Thus, the influence of fluorine on the performance of mid-T baked, nitrogen-doped and particularly mild-baked (120 ∘C/48 h) cavities must be considered. The possible role of fluorine in the educed Nb+5→Nb+4 reaction under the impact of an x-ray beam at room temperature and during the thermal treatment is also discussed. The range of temperature and duration parameters of the thermal treatment at which the niobium surface would not be contaminated with impurities is determined.

Redox Stability and Electrical Properties of a Series of Novel Quadruple Dopant BIMEVOX: Bi2V1−4x(CuNiNbTi)xO5.5−δ

Bi2VO5.5‐based materials are well‐known oxide ion conductors owing to their exceptionally high ionic conductivity. However, their poor phase and redox stabilities under a reducing atmosphere hinder their practical application as electrolytes for solid oxide fuel cells. Here, a series of novel quadruple metal‐doped bismuth vanadium system materials Bi2V1−4x(CuNiNbTi)xO5.5−δ (0 ≤ x ≤ 0.1) are prepared through a traditional solid state reaction method, aiming to enhance the phase and redox stability under reducing atmosphere. The results reveal that multiple‐metal‐doping can stabilize the tetragonal phase of Bi2VO5.5 to room temperature and show good phase and structural stabilities under inert or high oxygen partial pressure atmospheres, as well as pure oxide ion conduction which is slightly lower than that of the parent material. However, under a reducing environment, the Bi2V1−4x(CuNiNbTi)xO5.5−δ materials would still undergo a phase decomposition, yielding elemental bismuth impurity, and introducing strong electronic conduction. Thus, how to improve the phase and redox stabilities under the reducing atmosphere of the Bi2VO5.5‐based materials is still the endeavor direction in the future.

Phases, stabilities, and oxide ion conductions of multiple lanthanide and tungsten co–doped δ-Bi2O3-based materials: From low to high configuration entropy

In this work, a series of multiple lanthanide and tungsten co-doped fluorite structured (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 (x = 0.1, 0.2, 0.3, 0.4) and (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 materials were prepared by traditional solid-state reaction method. The phases, stabilities, and electrical properties of these materials were thoroughly studied. The results revealed that under high oxygen partial pressure, CO2, or inert atmospheres, all these samples had excellent long term thermal stability and chemical stability, and the samples of (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 (x = 0.1, 0.2, 0.3, 0.4) with low or mediate configuration entropies showed pure and high oxide ion conductivities, e.g. ∼2.6 × 10−2 S/cm at 600 °C for the sample x = 0.2. Whereas, for the (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 sample with high configuration entropy, pure ionic conduction occurred only within a narrow temperature range (700−750 °C) under the N2 atmosphere. Under strong reducing condition, only the high-entropy sample (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 showed high phase and chemical stabilities, but would introduce strong electronic conduction rise from the reduction of the high content W6+. While for (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 with low or mediate configuration, phase decompositions with impurities of Bi metal and HoH2 were observed under strong reducing atmosphere, accompany with obviously decreased conductivities. Therefore, we provided here a comprehensive understanding for the multiple components doped Bi2O3-based materials with configuration entropy from low to high on their phases, stabilities, and electrical properties, and suggested a new strategy for designing and stabilizing bismuth-oxide-based materials.

Continuous Hot‐Dip Galvanizing of Medium‐Manganese Third‐Generation Advanced High‐Strength Steels

The effects of process atmosphere oxygen partial pressure (pO2) on the preimmersion surface structures, interfacial reactive wetting products, and reactive wetting mechanisms of two prototype (0.15–0.20)C–(5.6–5.9)Mn–(0.4–1.9)Al–(1.1–1.5)Si–(0–0.6)Cr (wt%) third‐generation advanced high‐strength steels during continuous hot‐dip galvanizing are determined. In this study, the two‐stage thermal processing routes employed comprise an austenitization anneal followed by flash pickling and an intercritical anneal. All annealing treatments are conducted in a N2–5 vol% H2 process atmosphere with a controlled dew point. The substrates are austenitized at dew points of –30 or –10 °C, intercritically annealed at a dew point of –30, –10, or +5 °C, and then galvanized using a conventional 0.2 wt% Al (dissolved) bath. The preimmersion surfaces comprise a near‐pure Fe layer with dispersed nanoscaled oxide nodules. The primary reactive wetting mechanism is the direct wetting of the surface Fe, while oxide wetting, oxide cracking and liftoff, and oxide bridging by the liquid metal bath are secondary reactive wetting mechanisms. Zn ingress into the substrate via pores in the oxide network from selective dissolution during flash pickling is also noted. A well‐developed Fe2Al5–xZnx interfacial layer is observed for all metallic coating conditions. The resultant coatings show outstanding adherence after ASTM three‐point bend testing.

Combustion and energy release characteristics of LiF- and AP-modified B/JP-10 suspension fuels prepared using a two-solvent method

B/JP-10 suspension fuel has very high energy density and high application prospects, but energy release during its actual combustion is incomplete. In this study, the surfaces of boron nanoparticles were modified by coating the particles with LiF and AP using a two-solvent method. Thermogravimetric experiments show that the ignition temperature of boron decreases from 772°C to 599°C when the LiF coating amount is 20 wt%. In a laser ignition experiment, the AP-modified B/JP-10 suspension fuel displayed a relatively obvious "microburst" phenomenon at the end of the combustion process. The "microburst" intensifies as the amount of AP coating increases; this behavior has positive implications for the release of energy from the boron in the fuel. The oxidation of boron in 10 wt% LiF-modified fuel increased from 26.35% to 36.22% without an increase in the ambient oxygen partial pressure. AP modification increases not only the oxidation rate of boron in the fuel but also the amount of oxidizing gas produced by decomposition, and this increases the burning intensity of JP-10. LiF and AP modification can destroy the shell layer of the agglomerates formed by the combustion of suspended fuels. LiF makes it difficult to close the shell layer by reacting with B2O3 to form easily sublimated substances and flaky crystals. AP breaks the shell structure due to the high pressure generated by the "microburst", thus forming a porous configuration on the surface of the agglomerate.

Selective Oxidation of a Medium-Mn Third Generation Advanced High Strength Steel during Austenitizing and Intercritical Annealing

The effect of the simulated continuous galvanizing line N2−5 vol% H2 process atmosphere oxygen partial pressure (pO2) on the external and internal selective oxidation of a prototype medium-Mn third generation (3G) advanced high strength steel was determined during a two-stage heat treatment cycle (i.e., austenitizing and intercritical annealing) which had previously yielded 3G properties. Thick external oxides (∼200 nm) were observed after the austenitizing heat treatment, regardless of the process atmosphere pO2 employed. An intermediate flash pickling step was successful in reducing the external oxide thickness significantly (to ∼30 nm) along with revealing some extruded metallic Fe nodules on the surface. The austenitizing heat treatment also resulted in a solute-depleted surface layer with a minimum thickness of 2 μm. This solute-depleted layer inhibited the formation of external oxides during intercritical annealing, resulting in a surface similar to that observed after flash pickling comprising a near-pure Fe surface with isolated, nodular external oxides. These surfaces are promising in terms of successful reactive wetting of this prototype medium-Mn steel during subsequent continuous hot-dip galvanizing.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

Research progress on the mechanism of cerebral blood flow regulation in hypoxia environment at plateau

ABSTRACT The plateau is a special environment with low air pressure and low oxygen content. The average altitude of Qinghai-Tibet is 3,500 m, and the atmospheric oxygen partial pressure in most areas is lower than 60% of that at sea level. In order to adapt to the plateau low-oxygen environment, the human body has developed corresponding physiological structure and functions adjust. In the present review, the regulation mechanism of cerebral blood flow (CBF) under high-altitude environments was elaborated in eight aspects: the arterial blood gas, endogenous substances in the nerve and blood, the cerebral neovascularization, the hematocrit, cerebral auto-regulation mechanism, cerebrovascular reactivity, pulmonary vasoconstriction, and sympathetic automatic regulation, aiming to further explore the characteristics of changes in brain tissue and cerebral blood flow in a hypoxic environment.

The Contribution of M-dwarf Flares to the Thermal Escape of Potentially Habitable Planet Atmospheres

Abstract The habitability of planets around M dwarfs (≲0.5 M ⊙) can be affected by the X-rays + extreme UV (XUV) emission of these stars, with flares occasionally increasing the XUV flux by more than 2 orders of magnitude above quiescent levels. This wavelength range can warm and ionize terrestrial planets’ upper atmospheres, which expands the planetary radius and promotes atmospheric loss. In this work, we study the contribution of the XUV flux due to flares on the atmospheric escape of Earth-like planets orbiting M dwarfs through numerical simulations. We considered the first Gyr of planets with initial surface water abundances between 1 and 10 terrestrial oceans (TO), a small primordial hydrogen envelope (≤10−3 M ⊕), and with host-star masses between 0.2 and 0.6 M ⊙. In this parameter range, we find that flares can remove up to two TO more than nonflaring stars, which, in some cases, translates to a doubling of the total water loss. We also find that flaring can increase atmospheric oxygen partial pressures by hundreds of bars in some cases. These results were obtained by adding a new module for flares to the VPLanet software package and upgrading its atmospheric escape module to account for Roche lobe overflow and radiation/recombination-limited escape.

Desulfurization of molten steel with molten slag using the electrochemical method

The desulfurization in metallurgical process is electrochemical reaction in nature. Desulfurization using the electrochemical method was proposed with the CaO-MgO-Al2O3 molten slag covering molten steel. Effect of an applied external DC voltage, which varied from 0 to 8V, was discussed. The results indicated that sulfur in molten steel could be removed effectively with applied external voltage. According to the mechanism analyses of the desulfurization under the applied external voltage, kinetics formulae were developed, and the model calculated results that were in agreement with the experimental values. The transfer coefficient of sulfur in molten slag under electromigration conditions was approximately 2.09?10-5 m?s-1?V-1. The desulfurization of molten steel with molten slag can be promoted by increasing the applied voltage, reducing the partial pressure of atmospheric oxygen, strengthening the stirring intensity of the reaction system, and optimizing the composition and properties of the slag.

Triple oxygen isotope constraints on atmospheric O2 and biological productivity during the mid-Proterozoic

Reconstructing the history of biological productivity and atmospheric oxygen partial pressure (pO2) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating pO2 and productivity during the Proterozoic. O-MIF, reported as Δ'17O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes. Atmospheric O-MIF can be preserved in the geologic record when pyrite (FeS2) is oxidized during weathering, and the sulfur is redeposited as sulfate. Here, sedimentary sulfates from the ∼1.4-Ga Sibley Formation are reanalyzed using a detailed one-dimensional photochemical model that includes physical constraints on air-sea gas exchange. Previous analyses of these data concluded that pO2 at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on pO2 is essentially unconstrained by these data. Indeed, pO2 levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that pCO2 could have been lower) or if the Sibley O-MIF data were diluted by reprocessing before the sulfates were deposited. Our model also shows that, contrary to previous assertions, marine productivity cannot be reliably constrained by the O-MIF data because the exchange of molecular oxygen (O2) between the atmosphere and surface ocean is controlled more by air-sea gas transfer rates than by biological productivity. Improved estimates of pCO2 and/or improved proxies for Δ'17O of atmospheric O2 would allow tighter constraints to be placed on mid-Proterozoic pO2.

Improved ferroelectric and piezoelectric properties of (Na0.5K0.5)NbO3 ceramics via sintering in low oxygen partial pressure atmosphere and adding LiF

Dense ([Formula: see text][Formula: see text]NbO3 lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO2, [Formula: see text][Formula: see text] atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added ([Formula: see text][Formula: see text]NbO3 ceramics sintered in air and the low pO2-sintered pure ([Formula: see text][Formula: see text]NbO3 ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant [Formula: see text] is 125 pC/N, and the converse piezoelectric constant [Formula: see text]* is 186 pm/V. The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03, respectively. Under the measured electric field of 70 kV/cm, the remanent polarization is 25.9 [Formula: see text]C/cm2 and the coercive field is 13.9 kV/cm. Furthermore, if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO2 atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes.

Proof-of-concept thermoelectric oxygen sensor exploiting oxygen mobility of GdBaCo2O5+δ

In this paper, we demonstrate a proof-of-concept oxygen sensor based on the thermoelectric principle using polycrystalline GdBaCo2O5+δ, where 0.45 &amp;lt; δ &amp;lt; 0.55 (GBCO). The lattice oxygen in layered double perovskite oxides is highly susceptible to the ambient oxygen partial pressure. The as-synthesized GBCO sample processed in ambient conditions shows a pure orthorhombic phase (Pmmm space group) and a δ-value close to 0.5 as confirmed by x-ray diffraction Rietveld refinement. The x-ray photoelectron spectroscopy (XPS) shows a significant Co3+ oxidation state in non-octahedral sites in addition to Co3+ as well as Co4+ in octahedral sites. The insulator-to-metal transition (MIT) is observed at 340 K as seen from resistivity and Seebeck coefficient. The Seebeck coefficient shows a large change of 10–12 μV/K with a time constant of ∼20 s at 300 K, when the gas ambience is changed from 100% oxygen to nitrogen and vice versa. The diffusion of oxygen in the GdOδ planes leads to the hole doping, which is a dominant factor for a large change observed in the Seebeck coefficient. This is also evident from the higher fraction of oxidized Co4+ as seen from XPS measurements. The interfacial grain boundary in addition to the oxygen diffusion contributes to the change in Seebeck. The change in Seebeck coefficient is minimal in the metallic state due to an insignificant increase in the carrier concentration, but the response is fairly well and reproducible for stoichiometry δ = 0.5 ± 0.05 below MIT. This principle shall be of significant importance in designing oxygen sensors operational at room as well as cryogenic temperatures.

A persistently low level of atmospheric oxygen in Earth\u2019s middle age

Resolving how Earth surface redox conditions evolved through the Proterozoic Eon is fundamental to understanding how biogeochemical cycles have changed through time. The redox sensitivity of cerium relative to other rare earth elements and its uptake in carbonate minerals make the Ce anomaly (Ce/Ce*) a particularly useful proxy for capturing redox conditions in the local marine environment. Here, we report Ce/Ce* data in marine carbonate rocks through 3.5 billion years of Earth’s history, focusing in particular on the mid-Proterozoic Eon (i.e., 1.8 – 0.8 Ga). To better understand the role of atmospheric oxygenation, we use Ce/Ce* data to estimate the partial pressure of atmospheric oxygen (pO2) through this time. Our thermodynamics-based modeling supports a major rise in atmospheric oxygen level in the aftermath of the Great Oxidation Event (~ 2.4 Ga), followed by invariant pO2 of about 1% of present atmospheric level through most of the Proterozoic Eon (2.4 to 0.65 Ga).

Simultaneous reduction of multi-dimensional defects in Sn-excess BaSnO3 epitaxial films induced by surface chemical reconstruction

Multi-dimensional defects created by thermodynamic and mechanical condition strongly limit electron mobility by the scattering of charged carriers in semiconducting ${\mathrm{BaSnO}}_{3}$ (BSO) epitaxial films. Here, we demonstrate that the density of both extended and point defects in heteroepitaxial BSO films can be decreased simultaneously by exploiting surface phase instability and a subsequent redistribution of cations at thermal treatment under different oxygen chemical potentials. By delicately controlling both cation ratio and ambient oxygen partial pressure $p$(${\mathrm{O}}_{2}$), distinct surface topography and cation redistribution (i.e., BaO segregation or SnO evaporation) were observed along with effective healing of extended defects. Simultaneous control of extended and point defects in La-doped ${\mathrm{BaSnO}}_{3}$ (LBSO) films during treatment under reducing atmosphere decreased their scattering of charged carriers and yielded an increase in room-temperature electron mobility ${\ensuremath{\mu}}_{\mathrm{e}}$ by $\ensuremath{\sim}104%\phantom{\rule{0.16em}{0ex}}(55--112\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$ in initially Sn-excess LBSO films as a result of a complex interplay with the removal of Sn-related species at the surface. Our finding suggests a versatile strategy to further enhance electron transport of perovskite-type stannate films by exploiting chemical heterogeneity on the surface interfacing with the $p$(${\mathrm{O}}_{2}$)-controlled ambient.