High-pressure Oxygen Atmosphere Research Articles

Oxidation Behavior of Atmospheric Plasma Sprayed NiAl Coating at High Pressure Oxygen Atmosphere

The high-temperature and high-pressure oxygen-rich combustion gases often cause the high temperature gas conduit in rocket engine to suffer severe oxidation, resulting in a reduced service life. The present study deposited a dense NiAl coating on GH4202 superalloy using atmospheric plasma spraying and investigated its oxidation behavior in a high temperature and high-pressure oxygen atmosphere. The results showed that the NiAl coating presented excellent bonding with the superalloy substrate throughout tests. The uncoated GH4202 substrate was severely oxidized during high pressure oxygen atmosphere. It was found that only a continuous very thin Al2O3 oxide scale evolved on the NiAl coating surface and no oxidation was observed at the interface between the NiAl coating and GH4202 substrate. Moreover, no significant inner oxidation occurred to NiAl coating. Therefore, the present APS NiAl coating can provide effective protection of superalloy from oxidation at high pressure oxygen combustion gas atmosphere.

High-quality ferroelectric Bi0.5K0.5TiO3‒BiFeO3 solid-solution single crystals grown under high-pressure oxygen atmosphere

Ferroelectric (Bi0.5K0.5)TiO3–BiFeO3 solid solutions are promising materials for high-temperature piezoelectric applications because of their high depolarization temperature. In this study, we demonstrate the successful growth of high-quality (Bi0.5K0.5)TiO3–BiFeO3 single crystals near the morphotropic phase boundary by a flux method. Crystal growth at a high oxygen pressure of 0.9 MPa drastically reduces leakage currents, which enables ferroelectric polarization switching and a piezoelectric response associated with a rotation of polar nanosized domains. This study contributes to further detailed analyses of the relationship between crystal structures and ferroelectric properties of the (Bi0.5K0.5)TiO3–BiFeO3 solid-solution system.

NiCo2O4 films fabricated by reactive molecular beam epitaxy and annealing in various oxygen atmospheres

Nickel cobalt spinel oxide, NiCo2O4, is an important material for spintronics because it exhibits both ferrimagnetic characteristics and electrical conductivity. Because high oxygen pressure during deposition is necessary to obtain useful properties, pulsed laser deposition has been used to fabricate NiCo2O4 films. In this study, we investigated the physical properties of NiCo2O4 films synthesized by reactive molecular beam epitaxy and annealing in a high-pressure oxygen atmosphere. The characteristics of the films strongly depended on the oxygen pressure, and a larger pressure tended to give larger magnetization and higher conductivity. Crystal structure analysis by x-ray diffraction and transmission electron microscopy revealed that the films consisted of a rock salt (Ni,Co)O phase and a spinel NiCo2O4 phase. This phase separation caused the small magnetization and large electric resistance because the rock salt phase was an antiferromagnetic insulator.

Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi2Sr2CuO6 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy**Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0300300 and 2017YFA0302900, the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant Nos XDB07020300 and XDB25000000, the National Basic Research Program of China under Grant

By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi2Sr2CuO6+δ (Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with Tc covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from hole-like Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of ∼0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states. Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.

Ignition and Oxidation of Core–Shell Al/Al2O3 Nanoparticles in an Oxygen Atmosphere: Insights from Molecular Dynamics Simulation

This study employed the reactive force field molecular dynamics to capture atomic-level heat and mass transfer and reaction processes of an aluminum nanoparticle (ANP) oxidizing in a high temperature and pressure oxygen atmosphere, revealing detailed mechanisms for oxidation of ANPs. Temporal variations of temperature, density, mean square displacement, atom consumption rate, and heat release rate of ANPs have been systematically examined. In addition, the effects of environment on ANP oxidation were also evaluated. The results show that ANPs undergo four stages of preheating, melting, fast Al core, and moderate shell oxidations during the whole oxidation process. The Al core starts to melt from a core–shell interface with outward diffusion of core Al atoms into the shell. Intense reaction occurs between shell O and core Al atoms around the interface at the end of melting, leading to fast Al core oxidation. After complete oxidation of the Al core, the oxide shell continues to react with ambient O atoms. Both the initial environmental temperature and the equivalent pressure significantly influence the preheating. Conversely, the melting stage seems almost independent of any of them. However, fast Al core oxidation presents more sensitivity to the ambient equivalent pressure.

Enhanced polarization properties of ferrielectric AgNbO3 single crystals grown by Czochralski method under high-pressure oxygen atmosphere

We report crystal growth under high oxygen pressure (PO2) atmosphere that yields high-quality single crystals of AgNbO3. X-ray fluorescence analysis reveals that an increase in PO2 during crystal growth effectively suppresses the deficiency of Ag and then leads to low leakage currents. Single crystals grown via the Czochralski method at a PO2 of 0.9 MPa are demonstrated to show ferrielectric switching with enhanced polarization under electric fields along the [110] direction.

Shift of superconducting transition temperatures in magnetic superconductor RuSr2(Eu1.5Ce0.5)Cu2O10-d under influence of annealing in high pressure oxygen atmosphere

Shift of superconducting transition temperatures in magnetic superconductor RuSr2(Eu1.5Ce0.5)Cu2O10-d under influence of annealing in high pressure oxygen atmosphere

Growing LaAlO3/SrTiO3 interfaces by sputter deposition

Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting.

The Role of Atmosphere on Phase Transformations and Magnetic Properties of Ulvospinel

We have synthesized the antiferromagnetic mineral ulvospinel, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4,</sub> in Ar to assess the role of inert atmosphere on phase formation and magnetic properties. We report the role of atmosphere on a possible phase transition and the magnetic properties of this mineral. Atmosphere dependent transformations of ulvospinel are observed with increasing temperature. Oxidation of ulvospinel to form metastable titanomaghemite is shown to occur at 300° in atmospheric conditions. Only slight titanomaghematitzation was observed in samples transformed under pressure in in situ temperature dependent X-ray experiments. Formation of ilmenite and hematite from ulvospinel was observed under high temperature, high pressure, and low oxygen atmosphere conditions.

Non-conducting interfaces of LaAlO3/SrTiO3 produced in sputter deposition: The role of stoichiometry

We have investigated the properties of interfaces between LaAlO3 films grown on SrTiO3 substrates singly terminated by TiO2. We used RF sputtering in a high-pressure oxygen atmosphere. The films are smooth, with flat surfaces. Transmission electron microscopy shows sharp and continuous interfaces with some slight intermixing. The elemental ratio of La to Al, measured by the energy dispersive X-ray technique, is found to be 1.07. Importantly, we find these interfaces to be non-conducting, indicating that the sputtered interface is not electronically reconstructed in the way reported for films grown by pulsed laser deposition because of the different interplays among stoichiometry, mixing, and oxygen vacancies.

Determination of fluoride in plant material using microwave induced oxygen combustion

Fluorine is essential in human and/or animal nutrition, thus it is important to know its concentration in a diet. One of the important sources of fluorine for humans is tea, containing relatively high amounts of this trace element. A method for fluoride determination in various kinds of tea using microwave supported sample preparation in a high pressure oxygen atmosphere followed by potentiometry with a fluoride ion-selective electrode were described. The parameters of the microwave device for such combustion procedure were checked and optimised in order to find settings ensuring complete sample combustion and/or absorption of the analyte in the absorption solution. For the ion-selective electrode measurement, the technique of standard addition was chosen. The Nernstian slope of the fluoride ion-selective electrode was measured and calculated in the concentration range in which the potential of samples occurred. Concentrations of fluorides in tea in the range from 24.5 mg/kg to 254.5 mg/kg were found. In order to check the accuracy of the method certified reference materials were used. The precision expressed as the relative standard deviation ranged from 3.7% to 15.9%. The method is fast, accurate and reliable for this kind of analysis. &amp;nbsp;

Determination of fluoride in spices using microwave induced oxygen combustion

Fluorine is essential in human and/or animal nutrition; therefore, so it is important to know its concentration in a diet. One of the possible sources of fluorine for humans is spice, containing various amounts of this trace element. This work describes the method for fluoride determination in various kinds ofspices using microwave-supported sample preparation in high pressure oxygen atmosphere followed by potentiometry with a fluoride ion-selective electrode. Parameters of the microwave device for combustion procedure were checked and optimized in order to find settings ensuring complete sample combustion and/or absorption of the analyte in the absorption solution. For the ion-selective electrode measurement, the technique of standard straight line was chosen. Concentrations of fluorides in spices and spice blends under investigation ranged from 3.15 mg·kg-1 to 26.08 mg·kg-1. In order to check the accuracy of the method Certified Reference Material Fluoride in Vegetation NIST 2695 was used and a good agreement between certified and found values was found. The precision expressed as the relative standard deviation ranged from 0.6% to 5.0%. The method is fast, accurate and reliable for this kind of analysis. In recent literature data on fluoride concentrations in spices and/or spice blends have not been found.

Conductivity of LaAlO&lt;sub&gt;3&lt;/sub&gt;/SrTiO&lt;sub&gt;3&lt;/sub&gt; Interfaces Made by Sputter Deposition

There is much interest in interfaces between insulating oxides, such as SrTiO3 (STO) and LaAlO3 (LAO), where a two dimensional electron gas can form due to the so-called polar discontinuity. These interfaces are mostly fabricated by Pulsed Laser Deposition (PLD). We have investigated such interfaces by reactive RF sputtering in a high-pressure oxygen atmosphere. The films are smooth and crystalline. Transmission Electron Microscopy indicates that the interfaces are sharp and continuous while Electron Energy Loss Spectroscopy data indicate some slight intermixing. However, we find these interfaces to be non-conducting. It appears that the sputtered interface is not electronically reconstructed in the way reported for films grown by PLD, notwithstanding the good structural quality and composition of the films

Crystal Growth and Characterization of (Bi0.5Na0.5)TiO3–BaTiO3Single Crystals Obtained by a Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere

Crystal Growth and Characterization of (Bi_0.5Na_0.5)TiO₃–BaTiO₃Single Crystals Obtained by a Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere

Crystal Growth and Characterization of (Bi0.5Na0.5)TiO3–BaTiO3 Single Crystals Obtained by a Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere

A single crystal of ferroelectric 0.88(Bi,Na)TiO3–0.12BaTiO3 (BNT–BT) solid solution with tetragonal P4mm structure was grown by a top-seeded solution growth (TSSG) method at a high oxygen pressure (PO2 ) of 0.9 MPa. The crystals exhibited a large remanent polarization (Pr) of 54 µC/cm2, which leads to a spontaneous polarization estimated to be 54 µC/cm2. The large Pr compared with that of crystals grown at PO2 = 0.1 MPa is suggested to originate from a low oxygen vacancy concentration. The high-PO2 TSSG method is demonstrated to be effective for obtaining large-sized, high-quality BNT–BT crystals.

Growth and characterisation of LixCoO2 single crystals

Centimetre-size single crystals of LiCoO2 were successfully grown using a floating-zone method associated with an image furnace. A high-pressure oxygen atmosphere and a relatively small growth speed were found necessary to prevent the formation of impurity phases in the grown crystal. A single crystal with a reduced amount of lithium was obtained by means of the chemical de-lithiation process using as grown LiCoO2 single crystal as the starting material. Growth conditions together with magnetic and structural properties of these crystals are discussed here.

高圧酸素下溶液引き上げ法による(Bi0.5Na0.5)TiO3単結晶の育成と特性評価

高圧酸素下溶液引き上げ法による(Bi0.5Na0.5)TiO3単結晶の育成と特性評価

Effects of Defect Control on the Polarization Properties in Bi2WO6-Based Single Crystals

Leakage-current and polarization-switching properties of defect-controlled Bi 2 WO 6 single crystals have been investigated along the crystallographic a axis at 25°C. High-pressure oxygen annealing decreased leakage current, indicating that electron is a detrimental carrier of the leakage-current property. 2-mol% Mn substitution at the W site is shown to be effective for suppressing leakage current density to the order of 108 A/cm2. Mn-doped crystals annealed under high-pressure oxygen atmosphere showed a well saturated polarization hysteresis loop with a remanent polarization of 50 μC/cm2 and a coercive field of 39 kV/cm. It is found that high-pressure oxygen annealing is effective for decreasing coercive field of Mn-doped crystals due to less oxygen vacancies. It is concluded that Mn substitution and the subsequent oxygen annealing enhance polarization switching as well as reduce leakage current in the BW system.

Influence of Oxygen Vacancies on the Polarization Properties in Bi&lt;sub&gt;4&lt;/sub&gt;Ti&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; Ferroelectric Single Crystals

Measurements of the leakage-current and polarization properties in bismuth titanate (Bi4Ti3O12) along the a axis show that the crystals grown in air followed by air annealing at 700oC had a superior remanent polarization of 48 μC/cm2 as well as a low leakage current density of the order of 10-9 A/cm2. The annealing at a high oxygen partial pressure of 35MPa (700oC) resulted in a higher leakage current, indicating that electron holes arising from the incorporation of oxygen at oxygen vacancies act as detrimental carriers for electrical conduction at room temperature. A crystal growth under high-pressure oxygen atmosphere and subsequent annealing at a moderate oxygen partial pressure is proposed to be advantageous for suppressing the vacancy formation and for attaining a large remanent polarization as well as a high insulating property of the Bi4Ti3O12 system.

A study of the formation and oxidation of PtSi by SR–PES

In the paper we present the results on the formation of platinum silicide (PtSi) by means of synchrotron radiation photoelectron spectroscopy (SR–PES) and show the effect of a Pt/Si sample exposure to both a low and high-pressure oxygen atmosphere at the end of an annealing process. We have carried out a detailed analysis of high resolution photoelectron spectra of the Pt 4f and Si 2p peaks which were taken during the sample annealing at specific temperatures. In addition to the generally known Pt 2Si and PtSi phases we have recognized an additional intermediate phase during the formation of Pt 2Si and attributed it to the Pt 3Si phase. We have proved that silicon diffuses towards the sample surface. The results of a low-pressure oxygen experiment have shown that oxygen binds only to surface silicon, however, in the case of a PtSi sample prepared externally in the ON Semiconductor labs under nitrogen/oxygen atmosphere oxygen binds not only to surface silicon but also takes over Si atoms out of the PtSi phase which results in the formation of a SiO 2 layer on almost pure platinum.