High Oxygen Partial Pressure Research Articles

Oxygen Exchange and Transport in (La0.6Sr0.4)0.98FeO3-d – Ce0.9Gd0.1O1.95 Dual-Phase Composites

The chemical diffusion coefficient and the effective surface exchange coefficient (kex) of dual-phase (La0.6Sr0.4)0.98FeO3-d (LSF) − Ce0.9Gd0.1O1.95 (CGO) composites containing between 30 and 70 vol.% of CGO were determined by electrical conductivity relaxation (ECR) at high oxygen partial pressures (10−3 < pO2 < 1 atm) and at temperatures between 600°C and 900°C. The surface impurity segregation was detected by TOF-SIMS analysis. A large enhancement of kex was observed with increasing CGO fraction in the composite. kex was increased from 3.51 × 10−5 cm/s for a pure LSF to 1.86 × 10−4 cm/s for a 70 vol.% of CGO in the composite at 750°C for a pO2 change from 0.2 to 1.0 atm. The experiments demonstrate that the kex is enhanced due to a synergistic effect between the two phases, and suggest a direct involvement of CGO phase in the oxygen surface exchange reaction. Possible mechanisms that could account for the synergy are the oxygen exchange process occurs also on the CGO surface, for example a spillover of absorbed oxygen ions from the LSF surface to the CGO surface or/and scavenging of impurities from one phase to another, thereby improving the oxygen exchange properties of the cleaned phase.

Influneces of different oxygen partial pressures on switching properties of Ni/HfOx/TiN resistive switching devices

The HfOx-based resistive random access memory (RRAM) has been extensively investigated as one of the emerging nonvolatile memory (NVM) candidates due to its excellent memory performance and compatibility with CMOS process. In this study, the influences of deposition ambient, especially the oxygen partial pressure during thin film sputtering, on the resistive switching characteristics are discussed in detail for possible nonvolatile memory applications. The Ni/HfOx/TiN RRAMs are fabricated, and the HfOx films with different oxygen content are deposited by a radio frequency magnetron sputtering at room temperature under different oxygen partial pressures. The oxygen partial pressures in the sputter deposition process are 2%, 4% and 6% relative to engineer oxygen content in the HfOx film. Current-voltage (I-V) measurements, X-ray photoelectron spectroscopy, and atomic force microscopy are performed to explain the possible nature of the stable resistive switching phenomenon. Through the current-voltage measurement, typical resistive switching behavior is observed in Ni/HfOx/TiN device cells. It is found that with the increase of the oxygen partial pressure during the preparation of HfOx films, the stoichiometric ratio of O in the film is improved, the root mean square (RMS) of the surface roughness of the film slightly decreases due to the slower deposition rate under a higher oxygen partial pressure, and the high resistance state (HRS) current decreases. In addition, by controlling the oxygen content of the device, the endurance performance of the device is improved, which reaches up to 103 under a 6% oxygen partial pressure. The HfOx films prepared at a higher oxygen partial pressure supply enough oxygen ions to preserve the switching effect. As the oxygen partial pressure increases, the uniformity of the switching voltage is improved, which can be attributed to the fact that better oxidation prevents the point defects (oxygen vacancies) from aggregating into extended defects. Through the linear fitting and temperature test, it is found that the conduction mechanism of Ni/HfOx/TiN RRAM device cells in low resistance state is an ohmic conduction mechanism, while in high resistance state it is a Schottky emission mechanism. The interface between TE and the oxide layer (HfOx) is expected to influence the resistive switching phenomenon. The activation energy of the device is investigated based on the Arrhenius plots in HRS. A switching model is proposed according to the theory of oxygen vacancy conductive filament. Furthermore, the self-compliance behavior is found and explained.

Critical conditions for the formation of p-type ZnO with Li doping.

The stability of Li dopants in ZnO is studied via first-principles calculations with electric dipole correction. The formation energies of substitutional Li (LiZn), interstitial Li (Lii) and the LiZn + Lii complex are calculated in large supercells and the results are extrapolated to the limit of an infinite-sized supercell. The stabilities of 2LiZn and the LiZn + Lii complex are found to depend on the temperature and absolute oxygen partial pressure. At normal experimental temperature (900 K), an extremely high absolute oxygen partial pressure (194 bar) is needed to break the coupling between LiZn and Lii and thus form p-type ZnO. The reaction barrier and the absorbance spectra are also discussed.

Synthesis of low core loss Finemet/Ni0.5Zn0.5Fe2O4 composites by co-precipitation method

Finemet/Ni0.5Zn0.5Fe2O4 core/shell structure composites have been prepared by a co-precipitation method followed by a high temperature sintering process. The formation mechanism of the core/shell structures and the effects of oxygen partial pressure during the sintering process on the phase structure, microstructure, and magnetic properties were discussed. Low and high oxygen partial pressures resulted in the formation of crystal defects and a reduction of the magnetic properties of the composites. The magnetic properties could be adjusted by controlling the oxygen partial pressure and the optimal magnetic properties of the composites were obtained by sintering under an oxygen partial pressure of 10%. The resulting composite exhibited a high permeability of 61, a high saturation magnetization of 135.5 emu/g and a low core loss of approximately 30.5 mW/cm3 at 100 kHz and 100 mT.

Antioxidant responses and deregulation of epigenetic writers and erasers link oxidative stress and DNA methylation in bovine blastocysts.

Early mammalian embryos derived from in vitro fertilization are exposed to conditions distinct from the native oviduct-uterine environment, including atmospheric oxygen that promotes cellular oxidative stress and alters gene expression. High oxygen partial pressure during embryo development is associated with low pregnancy rates and increased embryonic apoptosis. We investigated how bovine embryos responded to high (20%) or low (5%) oxygen partial pressure during in vitro culture, evaluating levels of reactive oxygen species (ROS) as well as changes in the expression of oxidative stress- and epigenetic-related transcripts and miRNAs in blastocysts. Additionally, we determined the global DNA methylation levels in the resulting embryos. Our data indicated that bovine blastocysts produced in vitro under high oxygen partial pressure possessed elevated ROS abundance and exhibited increased expression of CAT, GLRX2, KEAP1, NFR2, PRDX1, PRDX3, SOD1, TXN, and TXNRD1, versus reduced levels of the oxidative stress-related bta-miR-210. These stressed embryos also presented altered expression of the epigenetic-associated transcripts DNMT3A, H2AFZ, H3F3B, HDAC2, MORF4L2, REST, and PAF1. In addition, we demonstrated that embryos cultured under high oxygen partial pressure have increased global DNA methylation, suggesting that DNA hypermethylation is mediated by the deregulation of epigenetic-related enzymes due to oxidative stress.

Direct Observation of Room-Temperature Stable Magnetism in LaAlO3/SrTiO3 Heterostructures.

Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO3 and SrTiO3 (LaAlO3/SrTiO3), striking interfacial magnetisms have been observed in LaAlO3/SrTiO3 heterostructures. Interestingly, the strength of the interfacial magnetic moment is found to be dependent on oxygen partial pressures during the growth process. This raises an important, fundamental question on the origin of these remarkable interfacial magnetic orderings. Here, we report a direct evidence of room-temperature stable magnetism in a LaAlO3/SrTiO3 heterostructure prepared at high oxygen partial pressure by using element-specific soft X-ray magnetic circular dichroism at both Ti L3,2 and O K edges. By combining X-ray absorption spectroscopy at both Ti L3,2 and O K edges and first-principles calculations, we qualitatively ascribe that this strong magnetic ordering with dominant interfacial Ti3+ character is due to the coexistence of LaAlO3 surface oxygen vacancies and interfacial (TiAl-AlTi) antisite defects. On the basis of this new understanding, we revisit the origin of the weak magnetism in LaAlO3/SrTiO3 heterostructures prepared at low oxygen partial pressures. Our calculations show that LaAlO3 surface oxygen vacancies are responsible for the weak magnetism at the interface. Our result provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective to understand magnetic and electronic reconstructions at such strategic oxide interfaces.

Effect of the preform fabrication process on the properties of all-silica optical fibres

In this paper, we present a detailed comparison of technical capabilities of processes for the fabrication of all-silica optical fibre preforms with the use of an atmospheric pressure radio frequency plasma (POVD process) and low-pressure microwave plasma (PCVD process) and analyse the origin of the difference in optical properties between fibres produced by these methods. It is shown that the higher temperature of the core material and the higher oxygen partial pressure in preform fabrication by the POVD process lead to an increase in optical losses in the visible and UV spectral regions in the silica fibres with low hydroxyl (OH) content and a decrease in the solarisation resistance of the fibres with high OH content, i.e. to a more rapid increase in background losses in response to UV irradiation. No such drawbacks are detected in the case of the growth of reflective layers by the PCVD process.

The effects of measuring atmosphere on ultraviolet photodetection performance of ZnO nanostructures

Herein, a comparative study focusing on the effects of measuring atmosphere on ultraviolet (UV) photodetection performance of ZnO nanostructures is presented. Various morphologies of ZnO nanostructures were synthesized by changing the hydrothermal temperature within 343–423 K. The ultraviolet photodetection performance of the samples was studied against dark ultraviolet light (360 nm, 800 μW/cm2) under 200 sccm gas flows of argon and oxygen. The nanoflowers grown at 373 and 393 K showed the best photosensitivity and photoresponsivity under both argon and oxygen flows. Concerning the importance of active surface area, it was shown that the sample grown at 393 K serves higher accessible surface-to-volume ratio (qualitatively observable by SEM and confirmed by BET), higher concentration of freed electron due to oxygen vacancies (confirmed by PL) and consequently, the best UV photosensitivity. The comparative study between photodetection parameters in argon and oxygen atmospheres showed that although higher partial pressure of oxygen is favorable for all photodetection parameters like photosensitivity, photoresponsivity and decay time, it has adverse effects on rising time because rising time is directly coupled with the density of desorbed oxygen atoms.

Stable LSM/LSTM bi-layer interconnect for flat-tubular solid oxide fuel cells

A bi-layer interconnect with La0.8Sr0.2MnO3 and La0.4Sr0.6Ti0.6Mn0.4O3 (LSM/LSTM) is applied to anode-supported button cells and flat-tubular cells. Using a button cell, SEM images and gas permeation tests confirm that the bi-layer possesses a dense microstructure. The area specific resistance (ASR) of the LSM/LSTM remains nearly constant under oxidizing/reducing atmospheres with varying gas concentrations. For comparison, an LSM/LST with the same thickness is prepared; an increase in the ASR is observed as the concentration of H2 feed to the LST side decreases. The difference in the ASR of LSM/LST can be explained by exposure to a relatively high oxygen partial pressure and partial destruction of the interfacial LST layer region where oxygen diffuses from the LSM layer. Flat-tubular cells with the LSM/LSTM bi-layer interconnect achieve a maximum power density (MPD) of 463 mW cm−2 using humidified H2 fuel and air at 800 °C. With decreasing H2 concentration in the fuel, the polarization resistance increases rather than the ohmic resistance, implying that the LSM/LSTM interconnect provides stable conduction property. In comparison with the conventional LSM/LST interconnect cell, it shows improved stability and performance as the concentration of H2 in the fuel decreases.

Oxygen partial pressure effects on the RF sputtered p-type NiO hydrogen gas sensors

NiO thin films were grown by Radio Frequency (RF) Magnetron Sputtering method under different oxygen partial pressures, which are 0.6 mTorr, 1.3 mTorr and 2.0 mTorr. The effects of oxygen partial pressures on the thin films were analyzed through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Hall measurements. The change in the surface morphology of the thin films has been observed with the SEM and AFM measurements. While nano-pyramids have been obtained on the thin film grown at the lowest oxygen partial pressure, the spherical granules lower than 60 nm in size has been observed for the samples grown at higher oxygen partial pressures. The shift in the dominant XRD peak is realized to the lower two theta angle with increasing the oxygen partial pressures. XPS measurements showed that the Ni2p peak involves satellite peaks and two oxidation states of Ni, Ni2+ and Ni3+, have been existed together with the corresponding splitting in O1s spectrum. P-type conductivity of the grown NiO thin films are confirmed by the Hall measurements with concentrations on the order of 1013 holes/cm−3. Gas sensor measurements revealed minimum of 10% response to the 10 ppm H2 level. Enhanced responsivity of the gas sensor devices of NiO thin films is shown as the oxygen partial pressure increases.

Growth dynamics controllable deposition of homoepitaxial MgO films on the IBAD-MgO substrates

Homoepitaxial MgO (Homo-MgO) films, deposited by RF magnetic sputtering method in various experimental conditions, were systematically studied using growth dynamics in older to fully understand their growth mechanism. The results showed that high quality Homo-MgO films could be obtained at high oxygen partial pressure and the thickness of Homo-MgO films were seriously affected by the ratio of O2/Ar. Moreover, an interesting phenomenon we addressed was the growth mode changed with varying the sputtering power, leading to different surface morphology. Most importantly, apart from Homo-MgO films, our theory can also be appropriate for other oxide films grown by RF magnetic sputtering technology.

Differential Effects of Temperature on Oxygen Consumption and Branchial Fluxes of Urea, Ammonia, and Water in the Dogfish Shark (Squalus acanthias suckleyi).

Environmental temperature can greatly influence the homeostasis of ectotherms through its effects on biochemical reactions and whole-animal physiology. Elasmobranchs tend to be N limited and are osmoconformers, retaining ammonia and urea-N at the gills and using the latter as a key osmolyte to maintain high blood osmolality. However, the effects of temperature on these key processes remain largely unknown. We evaluated the effects of acute exposure to different temperatures (7°, 12°, 15°, 18°, 22°C) on oxygen consumption, ammonia, urea-N, and diffusive water fluxes at the gills of Squalus acanthias suckleyi. We hypothesized that as metabolic demand for oxygen increased with temperature, the fluxes of ammonia, urea-N, and 3H2O at the gills would increase in parallel with those of oxygen. Oxygen consumption (overall [Formula: see text] from 7.5° to 22°C) and water fluxes (overall [Formula: see text]) responded to increases in temperature in a similar, almost linear, manner. Ammonia-N efflux rates varied the most, increasing almost 15-fold from 7.5° to 22°C ([Formula: see text]). Urea-N efflux was tightly conserved over the 7.5°-15°C range ([Formula: see text]) but increased greatly at higher temperatures, yielding an overall [Formula: see text]. These differences likely reflect differences in the transport pathways for the four moieties. They also suggest the failure of urea-N- and ammonia-N-conserving mechanisms at the gill above 15°C. Hyperoxia did not alleviate the effects of high temperature. Indeed, urea-N and ammonia-N effluxes were dramatically increased when animals were exposed to high temperatures in the presence of hyperoxia, suggesting that high partial pressure of oxygen may have caused oxidative damage to gill epithelial membranes.

Work function and surface stability of tungsten-based thermionic electron emission cathodes

Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W–Ba–O is the canonical materials system that functions as the thermionic electron emitter commercially used in a range of high-power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W–Ba–O system using density functional theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba–O species with compositions in the range of Ba0.125O–Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis and thus may exhibit surface orientation fractions well described by the calculated Wulff construction.

Influence of oxygen partial pressure adopted in separate heat-treatment steps on the epitaxy of LZO film

The influence of oxygen partial pressure on epitaxy is systematically studied in La2Zr2O7 (LZO) thin films fabricated by metal organic deposition (MOD) on yttria stabilized zirconia (00l) single crystal substrates. The results show that oxygen partial pressure affects not only the epitaxial growth but also the morphology evolution of film. It is observed that the texture sharpness of LZO film improves while its surface flatness becomes worse with increasing oxygen partial pressure during the whole heat-treatment process. Further studies illustrate that high oxygen partial pressure at pyrolysis step favors the texture sharpening of LZO film, which is contributed to the complete decomposition of organic constitution and the decrease of residual carbon in oxide film. However, low oxygen partial pressure at crystalline step helps the improvement of surface flatness for LZO thin film. It is supposed to be linked with the decrease of oxygen vacancy defects and the increase of grain size along with the replenishment of oxygen content at the crystallization stage. Tailoring oxygen partial pressure at separate heat-treatment steps is important to improving texture sharpness and surface flatness of LZO buffer film as long as the oxidation of metallic substrate can be avoided in coated conductors.

An ab initio study of hydroxylated graphane.

Graphene-based derivatives with covalent functionalization and well-defined stoichiometry are highly desirable in view of their application as functional surfaces. Here, we have evaluated by ab initio calculations the energy of formation and the phase diagram of hydroxylated graphane structures, i.e., fully functionalized graphene derivatives coordinated with -H and -OH groups. We compared these structures to different hydrogenated and non-hydrogenated graphene oxide derivatives, with high level of epoxide and hydroxyl groups functionalization. Based on our calculations, stable phases of hydroxylated graphane with low and high contents of hydrogen are demonstrated for high oxygen and hydrogen partial pressure, respectively. Stable phases of graphene oxide with a mixed carbon hybridization are also found. Notably, the synthesis of hydroxylated graphane has been recently reported in the literature.

Synthesis and characterization of Sr0.75Y0.25Co0.9Ru0.1O3−δ perovskite as a solid oxide fuel cell cathode material

The oxygen-deficient Sr0.75Y0.25Co0.9Ru0.1O3−δ (SYCR) cathode is systematically evaluated for the application of solid oxide fuel cells. X-ray diffraction analysis indicates that SYCR presents a tetragonal structure with space group of I4/mmm (139). In the measured high oxygen partial pressure (pO2) region (0.01–0.21 atm), the conductivity increases with increasing pO2 because of the oxygen vacancy annihilation and hole creation, relating to a general p-type semiconducting mechanism. To get an insight into the rate-limiting step of SYCR cathode, behaviors of individual polarization resistance (R 1 and R 2) are investigated in different pO2. The obtained fitting results reveal that R 1 is nearly independent on the pO2, while R 2 presents a (pO2)−0.5 dependence. At 800 °C, SYCR cathode exhibits an R p value of 0.14 Ω cm2, moreover, when using the wet hydrogen (∼ 3% H2O) as fuel and ambient air as oxidant, the maximum power density of single cell Ni-YSZ (yttria-stabilized zirconia)|YSZ|SYCR reaches 452.9 W cm−2.

中心静脈血酸素分圧値400 mmHgを呈した腹部大動脈瘤破裂の1症例：ultrasound guided内頸静脈穿刺の有用性

中心静脈血酸素分圧値400 mmHgを呈した腹部大動脈瘤破裂の1症例：ultrasound guided内頸静脈穿刺の有用性

“One-Pot” Solar Fuels

Chemists have always taken great pride in simplifying a complex multistep chemical synthesis into a single step process, in just one reactor. The motivation for doing so, apart from demonstrating synthetic competency and elegance, is the pursuit of green and sustainable solutions to chemical problems, as single step strategies have the inherent advantage of being atomically, energetically and economically efficient, as well as environmentally friendly and responsible.

Self-healing atmospheric plasma sprayed Mn1.0Co1.9Fe0.1O4 protective interconnector coatings for solid oxide fuel cells

Dense coatings on metallic interconnectors are necessary to suppress chromium poisoning of SOFC cathodes. Atmospherically plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective layers demonstrated reduced chromium related degradation in laboratory and stack tests. Previous analyses revealed strong microstructural changes comparing the coating's as-sprayed and operated condition. This work concentrates on the layer-densification and crack-healing observed by annealing APS-MCF in air, which simulates the cathode operation conditions. The effect is described by a volume expansion induced by a phase transformation. Reducing conditions during the spray process lead to a deposition of the MCF in a metastable rock salt configuration. Annealing in air activates diffusion processes for a phase transformation to the low temperature stable spinel phase (T < 1050 °C). This transformation is connected to an oxygen incorporation which occurs at regions facing high oxygen partial pressures, as there are the sample surface, cracks and pore surfaces. Calculations reveal a volume expansion induced by the oxygen uptake which seals the cracks and densifies the coating. The process decelerates when the cracks are closed, as the gas route is blocked and further oxidation continues over solid state diffusion. The self-healing abilities of metastable APS coatings could be interesting for other applications.

Failure analysis of leakage caused by perforation in an L415 steel gas pipeline

The reasons for the failure of a buried pipeline perforated during construction were investigated by a chemical composition analysis; a metallographic test; macromorphology observation; characterization of the corrosion products by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; field medium characterization; and an analysis of the working conditions. The results revealed that the material composition and organization of the steel pipe conformed to API Specification 5CT. However, the reason for the perforation of the L415 steel pipe was an ultrahigh growth rate of pitting corrosion, as high as 14mm per year. We confirmed that the synergistic effect of a high partial pressure of oxygen introduced by an improper packing process and concentrated Cl− in the corrosion product layer, which originated from groundwater with a high salt concentration that was used for the water pressure test, were responsible for the failure process.