Varying Oxygen Partial Pressure Research Articles

Charge Transport in the A6B2O17 (A = Zr, Hf; B = Nb, Ta) Superstructure Series

The electrical properties of the entropy stabilized oxides: Zr6Nb2O17, Zr6Ta2O17, Hf6Nb2O17 and Hf6Ta2O17 were characterized. The results and the electrical properties of the products (i.e. ZrO2, HfO2, Nb2O5 and Ta2O5) led us to hypothesize the A6B2O17 family is a series of mixed ionic-electronic conductors. Conductivity measurements in varying oxygen partial pressure were performed on A6Nb2O17 and A6Ta2O17. The results indicate that electrons are involved in conduction in A6Nb2O17 while holes play a role in conduction of A6Ta2O17. Between 900 °C–950 °C, the charge transport in the A6B2O17 system increases in Ar atmosphere. A combination of DTA/DSC and in situ high temperature X-ray diffraction was performed to identify a potential mechanism for this increase. In-situ high temperature X-ray diffraction in Ar does not show any phase transformation. Based on this, it is hypothesized that a change in the oxygen sub-lattice is the cause for the shift in high temperature conduction above 900 °C–950 °C. This could be: (i) Nb(Ta)4+- oxygen vacancy associate formation/dissociation, (ii) formation of oxygen/oxygen vacancy complexes (iii) ordering/disordering of oxygen vacancies and/or (iv) oxygen-based superstructure commensurate or incommensurate transitions. In-situ high temperature neutron diffraction up to 1050 °C is required to help elucidate the origins of this large increase in conductivity.

Perovskite stannate La-doped BaSnO3 films for near- and mid-infrared plasmonic applications

La-doped BaSnO3 (LBSO) epitaxial thin films were grown on (001) MgO substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target. The structural, electrical, and optical properties of the LBSO films were investigated as a function of oxygen pressure during deposition. The carrier mobility can be tuned from 13 cm2V−1s−1 to 44 cm2V−1s−1 by varying oxygen partial pressure from 2 Pa to 12 Pa, respectively. This improved mobility is attributed to the reduced film strain via reducing oxygen defect concentration or reducing off-stoichiometry in the film. The optical permittivity of LBSO films can also be modified as a function of the oxygen pressure during deposition, allowing tuning of their epsilon-near-zero wavelength from 1.9 µm to 5.6 µm. These results demonstrate that LBSO thin films grown on MgO can be used for plasmonic devices at mid-wave infrared wavelengths.

Copper Separation From Slag in Varying Oxygen Partial Pressures During Converting

Copper Separation From Slag in Varying Oxygen Partial Pressures During Converting

Study on the intrinsic defect in [formula omitted] crystal from combined first-principles and thermodynamic calculation

Erbium oxide (Er2O3) crystal is expected to be a new generation of persistent luminescence devices. The intrinsic point defects have a great influence on the properties of crystals. So, we investigated the formation energy of intrinsic point defect in Er2O3 crystal by density functional theory (DFT) and thermodynamic calculation. The effect of vibration entropy variation with temperature is considered. The results show that the influence of vibrational entropy on the formation energy should not be ignored under high-temperature. The defect formation energy under varied temperatures and oxygen partial pressure has been obtained. The results indicate that the most stable defect change from oxygen vacancies to erbium vacancies when the Fermi level increases from valence band maximum (VBM) to conduction band minimum (CBM). Erbium vacancies are predicted as shallow level acceptors. Fermi pinning effect causes the crystal to have a p-type conductive behavior. Our calculated result can provide the optimization condition for adjusting the main defect types to satisfy the needs of application.

Correlation between conductivity and structural parameters in Sr-doped LaMO3 (M = Al, Ga, In, Er, and Y) for solid oxide membranes

To understand the effect of the B site species in La-based perovskites, the electrical conductivity of La0.9Sr0.1MO3-δ (M = Al, Ga, In, Er, and Y) was studied under varying oxygen partial pressures ranging from 600 and 800 °C under humidified and dry conditions. The oxygen-ion conductors La0.9Sr0.1AlO3-δ and La0.9Sr0.1GaO3-δ exhibited no significant change in conductivity under humidified and dry conditions. In contrast, the mixed-ion conductor La0.9Sr0.1InO3-δ (LSI) and proton conductors La0.9Sr0.1ErO3-δ (LSEr) and La0.9Sr0.1YO3-δ (LSY) exhibit relatively significant changes under humidified and dry conditions. In addition, the conductivities of LSEr and LSY could be affected by the concentration of CO used to reduce the conductivity. Finally, this study demonstrated that as the unit cell volume divided by Z increased, the ionic conductivity changed from an oxygen ion conductor to a mixed conductor, and finally to a proton conductor.

ЭЛЕКТРОПРОВОДЯЩИЕ ХАРАКТЕРИСТИКИ ШЕЕЛИТОПОДОБНЫХ СИСТЕМ НА ОСНОВЕ МОЛИБДАТОВ КАЛЬЦИЯ И СТРОНЦИЯ

Strontium and calcium molybdates doped with bismuth and vanadium were synthesised by a conventional solid state method. The total electrical conductivity of the compositions was studied by impedance spectroscopy in the temperature range of 300–650 °С. The highest electrical conductivity is shown by solid solutions based on strontium molybdate. To estimate the contribution of electronic conductivity, measurements of the total electrical conductivity were made at various partial pressures of oxygen.

Structural and electrochemical studies of WO3 coated TiO2 nanorod hybrid thin films for electrochromic applications

This work presents the fabrication of Titanium dioxide (TiO2) nanorods/Tungsten oxide (WO3) hybrid thin films and the influence of nanostructures on the electrochromic behavior of the films. WO3 thin films were deposited at a constant substrate temperature of 673 K under various partial pressures of oxygen (ppO2). Also, Tungsten nanorods were grown on Fluorine doped tin oxide (FTO) coated glass substrate by hydrothermal process. Optimized WO3 films were coated on the TiO2 nanorod film by a sputter deposition method. Material, optical, electrical, and electrochemical analysis have been performed on the films using XRD, Raman, XPS, UV-Visible spectrometer and Cyclic voltammetry. The enhanced coloration efficiency (η) of the optimized WO3 films is found to be attributed to its large active surface area which favored H+ ions intercalation in the films. Also, the TiO2 nanorods/WO3 hybrid films exhibited a good electrochemical property in terms of the diffusion coefficient of 1.8 × 10−7 cm2/s better than those of pure WO3 and TiO2 nanorods.

Influence of oxygen on the optical, electrical, and heating properties of gallium-doped zinc oxide (GZO) films

Thin-film transparent heaters (TFTHs) are gaining popularity in optoelectronics and a variety of domestic applications, including smart windows, car defrosters, and other devices. The deposition and characterization of TFTHs made of gallium-doped zinc oxide (GZO) are presented in this work. GZO thin films were deposited via pulsed laser deposition on glass substrates with varying oxygen partial pressures from 0 to 10 mTorr during deposition. The samples demonstrated very low sheet resistance values between 5 and 17 Ω/sq from 0 to 10 mTorr, respectively. UV/vis transmission spectra revealed that TFTHs have a high optical transparency above 80%. GZO-based TFTHs demonstrated a consistent and repeatable joule heating effect, with temperatures reaching 76 °C with a low input voltage of 10 V. This research could guide the future use of GZO as a transparent conducting oxide material for many potential cost-effective applications from low-powered electronics to lightweight and wearable devices.

Intrinsically strained hexagonal Sr0.6Ba0.4MnO3 oxygen partial pressure dependent texturing and weak ferromagnetic behavior

We have probed the effect of intrinsic strain on the structural and magnetic properties of magneto-electric hexagonal Sr0.6Ba0.4MnO3 (SBMO) thin film grown by pulsed laser deposition on LaAlO3 (110) substrate by varying oxygen partial pressure (OPP). While the grown films show hexagonal structure with varying OPP, transition from oriented to polycrystalline growth is observed with increase in OPP. Raman spectroscopy confirms the P63/mmc symmetry of grown films along with the indication of distortion of octahedral. Magnetization measurements reveal room temperature weak ferromagnetic behavior in the thin films, which is in contrast to antiferromagnetic nature of its bulk counterpart. X-ray magnetic circular dichroism measurement confirms weak ferromagnetic behavior with contribution from unquenched orbital magnetic moment.

Kinetics of oxygen sorption-desorption processes in manganites of La0.7Sr0.3Mn0.9Fe0.1O3-δ composition

Based on the data of thermogravimetric analysis the values of the oxygen index (3-δ) in the manganite of the La0.7Sr0.3Mn0.9Fe0.1O3-δ composition, obtained by solid-phase reaction technique, have been calculated. The analysis of oxygen sorption-desorption curves showed that the processes of oxygen release and absorption at pO2 = 10 Pa and pO2 = 400 Pa are not reversible. The minima of the derivative dδ/dt = f (T) corresponding to the maxima of the oxygen extraction rate indicate the complex character of changes in the oxygen desorption rate from manganite. The decrease in the heating and cooling rate from 6.6 K/min to 2.6 K/min resulted in a significant change in the value ∆δ, indicating the dependence of anion mobility on the oxygen concentration in the magnet structure. It has been revealed that in the La0.7Sr0.3Mn0.9Fe0.1O3-δ manganite the oxygen desorption kinetics is well described by the exponential dependence on the Kramers model, which implies no return of desorbed oxygen to the sample. This model indicates the non-stationarity of the diffusion flux through the barrier during desorption of oxygen from samples. The calculation of the activation energy of oxygen desorption by the Merzhanov method at various partial pressures of oxygen has shown that at the initial stage of oxygen extraction from La0.7Sr0.3Mn0.9Fe0.1O3-δ, the activation energy of oxygen desorption has a minimum value (Еа = 103.7 kJ/mol at δ = 0.005) and as the concentration of oxygen vacancies increases, it rises reaching saturation (Еа = 134.3 kJ/mol at δ = 0.06). It is assumed that with an increase in the concentration of oxygen vacancies, an interaction occurs between them, followed by the processes of their ordering with the formation of associates.

A Thermogravimetric Temperature-Programmed Thermal Redox Protocol for Rapid Screening of Metal Oxides for Solar Thermochemical Hydrogen Production

As combinatorial and computational methods accelerate the identification of potentially suitable thermochemically-active oxides for use in solar thermochemical hydrogen production (STCH), the onus shifts to quickly evaluating predicted performance. Traditionally, this has required an experimental setup capable of directly carrying out a two-stage thermochemical water-splitting process. But this can be a difficult endeavor, as most off-the-shelf equipment cannot adequately deal simultaneously with the high temperatures, varying oxygen partial pressures, and high H2O partial pressures required; achieving sufficient temporal sensitivity to accurately quantify the kinetics is also a major challenge. However, as proposed here, a less complicated experiment can be used as a first screening for thermochemical water splitting potential. Temperature-Programmed Thermal Redox (TPTR) using thermogravimetry evaluates the thermal reduction behavior of materials. This technique does not require water splitting or CO2-splitting analogs but can nonetheless predict water-splitting performance. Three figures of merit are obtained from the TPTR experiment: reduction onset temperature, extent of reduction, and extent of recovery upon reoxidation. These metrics can collectively be used to determine if a material is capable of thermochemical water-splitting, and, to good approximation, predict whether the thermodynamics are favorable for use under more challenging high-conversion conditions. This paper discusses the pros and cons of using TPTR and proposes a protocol for use within the STCH community.

Understanding the Increasing Trend of Sensor Signal with Decreasing Oxygen Partial Pressure by a Sensing-Reaction Model Based on O2- Species.

Although the increasing trend of sensor signal with decreasing oxygen partial pressure was observed quite early, the underlying mechanism is still elusive, which is a hindrance to accurate gas detection under varying oxygen partial pressure. In this work, a sensing model based on previous experimental and theoretical results is proposed, in which the O2- species is determined to be the main oxygen species because O- species has not been observed by direct spectroscopic studies. On this basis, combined with the band bending of SnO2 at different oxygen partial pressures, the functional relationship between the surface electron concentration, oxygen partial pressure, and reducing gas concentration is established, which includes three forms corresponding to the depletion layer, accumulation layer, and flat band. In the depletion layer case, the variation of the sensor resistance to different concentrations of CO and oxygen can be well fitted with our function model. Besides, this model predicts that the response of sensors will no longer maintain the increasing trend in an extremely hypoxic atmosphere but will decrease and approach 1 with the background oxygen content further going down to 0.

Consequences of variation in oxygen partial pressure on zirconium oxide thin films

RF magnetron sputtering was used to deposit zirconium oxide thin films with oxygen as the reactive gas and argon as the inert gas. The effect of increasing the oxygen partial pressure from 17.0 to 50.0% on the structural, optical, wettability, and tribological properties of deposited films was examined. X-ray diffraction was used to characterize the structure of ZrO2 thin films, confirming the presence of a (1 1 1) peak whose intensity increases as the oxygen partial pressure decreases. Atomic force microscopy results indicate increase in surface smoothness values with decrease in oxygen partial pressure. Within the wavelength range of 300 nm to 700 nm, average transmittance values of roughly 80% were reported, demonstrating that zirconium oxide thin films are transparent. When utilizing a contact angle goniometer to measure contact angles for water and formamide liquids, the results show that the films are hydrophobic. The highest contact angle observed on zirconium oxide thin films are 102.6° and 101.3° for water and formamide liquids respectively. Tribological investigation shows that zirconium oxide thin films coated pins had a reduction of wear when compared to the uncoated pins.

Effect of annealing and oxygen partial pressure on the RF sputtered WO3 thin films for electrochromic applications

the electrochromic thin layer of Tungsten trioxide (WO3) was RF sputtered on FTO (fluorine-doped tin oxide) slide. In a reactive Ar + O2 gas environment with varying oxygen partial pressures, the deposition continued. The samples were air annealed at 400 °C for 2 h after being deposited at room temperature. SEM, XRD, UV–Visible spectrometer, and electrochemical analyzer characterization methods were employed to analyze the surface, structural morphology, optical, and electrochromic behaviour of the deposited material after annealing. The Optical Bandgap and Transmittance were found to be of a higher value for air annealed samples than RT deposited samples because RT deposited samples are amorphous whereas air annealed samples exhibit crystalline nature with Oxidation, reduction peak currents variation with respect to the temperature.

Partial redox cycling of composite storage materials for rechargeable oxide batteries

The redox behavior of Fe2NiO4/YSZ composites for application as oxygen storage material in rechargeable oxide batteries (ROBs) is investigated by means of thermogravimetric experiments in varying oxygen partial pressures, chosen to simulate the expected redox conditions that would occur during the operation of a ROB. The thermodynamic window of operation limits the oxidation to the formation of magnetite, as a continuation towards the nickel iron spinel or hematite risk compromising the anode of the ROBs solid oxide cell unit by exceeding the Ni/NiO redox equilibrium. The resulting mass change curves of the partial cycling showed no significant signs of capacity fading for the 104 cycles investigated, in addition to showing signs of increasing initial oxidation kinetics. Furthermore, evaluation of the oxidation process by means of Johnson-Mehl-Avrami-Kolmogorow (JMAK) equations was conducted. The resulting kinetic and geometric parameters are related to the microstructural development of the samples obtains by scanning electron microscopy (SEM) images, providing insights into the oxidation processes that result in the stable redox cycling of the material. The work expands on a previous study where the general redox behavior of the material was investigated with oxidations in air.

Post-Operative Monitoring of Intestinal Tissue Oxygenation Using an Implantable Microfabricated Oxygen Sensor.

Anastomotic leakage (AL) is a common and dangerous post-operative complication following intestinal resection, causing substantial morbidity and mortality. Ischaemia in the tissue surrounding the anastomosis is a major risk-factor for AL development. Continuous tissue oxygenation monitoring during the post-operative recovery period would provide early and accurate early identification of AL risk. We describe the construction and testing of a miniature implantable electrochemical oxygen sensor that addresses this need. It consisted of an array of platinum microelectrodes, microfabricated on a silicon substrate, with a poly(2-hydroxyethyl methacrylate) hydrogel membrane to protect the sensor surface. The sensor was encapsulated in a biocompatible package with a wired connection to external instrumentation. It gave a sensitive and highly linear response to variations in oxygen partial pressure in vitro, although over time its sensitivity was partially decreased by protein biofouling. Using a pre-clinical in vivo pig model, acute intestinal ischaemia was robustly and accurately detected by the sensor. Graded changes in tissue oxygenation were also measurable, with relative differences detected more accurately than absolute differences. Finally, we demonstrated its suitability for continuous monitoring of tissue oxygenation at a colorectal anastomosis over a period of at least 45 h. This study provides evidence to support the development and use of implantable electrochemical oxygen sensors for post-operative monitoring of anastomosis oxygenation.

Study of the electronic structure of Ce0.95Fe0.05O2-δ thin film using X-ray photoelectron spectroscopy

In the present work, the effect of the oxygen partial pressure (OPP) has been studied on the electronic structure of the Ce0.95Fe0.05O2-δ thin film (TF) through Raman spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The varying OPP, from 200 mTorr to 1 mTorr, was observed to vary the oxidation conditions during TF deposition. The oxygen valency was estimated to be reduced along with the generation of oxygen vacancies as determined via Raman analysis. The AFM analysis revealed the lowered values of the roughness parameters which indicated that reduction in OPP is associated with the smoothness of the film surface. The film surface was found to be reduced, as characterized by XPS investigation, as a result of the change in valency of Ce from +4 to +3 due to reduced OPP. The concentration of Ce3+ state was estimated to increase from 19.5% to 33% with reducing OPP. This evidently supports the formation of oxygen vacancies since the reduction of the valence state of Ce is known to be accompanied by the generation of oxygen vacancies. The O1 s spectra confirmed the oxygen non-stoichiometry as a function of OPP, whereas, Fe 2p suggested the mixed-valence state of Fe (Fe2+/Fe3+) in Ce0.95Fe0.05O2-δ (TF). To put in brief, the variation in OPP affects the chemical composition of the material by modifying its electronic structure via controlling the exchange interactions in the core structure of the compound.

Evolution of the microstructure of sputter deposited TaAlON thin films with increasing oxygen partial pressure

Abstract Recently, quaternary oxynitrides of transition metals and aluminum have attracted increasing interest due to their tunable properties. Within the present work, a series of TaAl(O)N films was sputter deposited using constant nitrogen and varying oxygen partial pressures. The films were grown from single element Ta and Al targets. The deposition parameters were adjusted to obtain a Ta/Al atomic ratio of ~50/50 for the oxygen-free film and were held constant for the following depositions, with the exception of the increasing oxygen partial pressure and compensatory decreasing argon partial pressure. Elastic recoil detection analysis revealed oxygen contents of up to ~26 at.%, while the nitrogen content decreased from ~47 at.% in the oxygen-free film to ~35 at.% in the film with the highest oxygen content, resulting in a significant decrease of the metal/non-metal ratio with increasing oxygen partial pressure. The micro- and bonding structures of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. All films exhibited a dominating face-centered cubic TaN-based structure with indications for additional nanocrystalline and amorphous phase fractions in the oxygen containing films. In addition, the mechanical properties were evaluated by nanoindentation, yielding a decreasing hardness and elastic modulus with increasing oxygen content.

Synthesis and equilibrium oxygen nonstoichiometry of PrBaFe2O5+w

A double-cell perovskite PrBaFe2O5+w is synthesized and its equilibrium nonstoichiometry investigated after quenching from flowing gas of varied oxygen partial pressures and temperatures. Whereas w ​= ​0 is reached at 856 ​°C in wet H2 of pH2O ​= ​0.02 ​bar yielding pO2 ​= ​4×10−21 ​bar, w ​= ​0.75 obtains at 400 ​°C in O2. Below ~1000 ​°C, compositions with w ​≥ ​0.5 order into a Cmmm superstructure that fully converts back upon heating to 1020 ​°C. PrBaFe2O5 of all equivalent Fe2.5+ sites orders into Fe2+ and Fe3+ upon cooling through a first-order transition at 204 ​K, with a 2 ​K hysteresis, as investigated by powder X-ray diffraction and differential scanning calorimetry. The valence-mixed and charge-ordered structures are refined from synchrotron X-ray powder diffraction patterns. The nonstoichiometry w is expressed as a function of T and pO2 of the flowing gas in a formal donor-dopant defect model via least-squares fit of thermodynamic parameters for point-defect equilibria in the solid.

O2-oxidation of individual graphite and graphene nanoparticles in the 1200–2200 K range: Particle-to-particle variations and the evolution of the reaction rates and optical properties

The kinetics for O2 oxidation of individual graphite and graphene platelet nanoparticles (NPs) were studied as a function of temperature (1200–2200 K) at varying oxygen partial pressures, using a single nanoparticle mass spectrometry method. NP temperature (TNP) was measured by measuring the NP thermal emission spectra during the kinetics studies. The initial oxidation efficiency is found to peak in the 1200–1500 K range, dropping by an order of magnitude as TNP was increased above 2000 K. There were large NP-to-NP variations in the oxidation rates, attributed to variations in the NP surface structure. In addition, the oxidation efficiencies evolved, non-monotonically, as the NPs reacted, decreasing by factors of between 10 and 300. This evolution of reactivity is attributed to changes in the NP surface structure due to the combination of oxidation and annealing. The optical properties, including wavelength dependence of the emissivity and the absorption cross section for the 532 nm heating laser, also tended to evolve as the NPs oxidized, but differently for each individual NP, presumably reflecting differences in the initial structures and their evolution.