Different Partial Pressures Of Oxygen Research Articles

Growth and Studies of Calcium Doped Laser Ablated Barium Titanate Thin Films

Ba1 − xCaxTiO3 targets were prepared by conventional solid state reaction with varied amounts of the calcium content (5 at.%, 10 at.%) and the thin films were deposited on Pt(111) coated Si substrate using pulsed laser ablation technique. The thin films were deposited at different pressures and temperatures, so as to determine the optimized growth parameter for the good quality BCT thin films. The pressure variation on the growth parameters made a dramatic impact in tailoring the dielectric constant and phase transition. The phase evolution of the BCT thin films evolves from 450°C and at higher substrate temperatures (∼700°C) for different partial pressures of oxygen, the preferred orientation of the thin films were observed. The SIMS analysis reveals a sharp interface exist at the bottom electrode (Pt)–BCT thin films indicating no interdiffusion taking place which might lead to the degradation of devices. The BCT thin films deposited at higher pressures (>60 mtorr) exhibited higher Ba content indicating the possibility of the Ca occupying the Ti site and is reflected in the decrease of the dielectric phase transition temperature. The ferroelectric hysteresis and Capacitance voltage measurement shows the signature of ferroelectricity.

Study on electrochromic performances of amorphous WO3 films

A series of WO3 films are prepared by rf-sputtering under different partial pressures of oxygen. It is found that the films with oxygen partial pressure ratio 1∶10 have better electrochronic(EC) properties than others. Microstructural and compositional characteristics of WO3 films are studied by x-ray diffraction, atomic force microscopy and x-ray photo electro spectroscopy. It is obvious that the samples are amorphous and have more pores that are beneficial for Li+ to inject and eject. The original-state films are composed of tungsten and oxygen. After electrochemical reactions， the main component becomes LixWO3 in which tungsten ions normally exhibit both W6+ and W5+ oxidation states. The films are annealed in air at 230 and 400℃ for 90 min. The cyclic voltammograms and optical transmittance show that the films annealed at 400℃ after more than 10 cycles present better EC properties.

Kinetic aspects of the formation of aluminium oxide by use of a microwave-induced plasma.

The oxidation of thin aluminium layers in a microwave plasma has been investigated to determine the kinetics of oxide growth. Thin Al-coatings were oxidized by means of a variety of gas mixtures, characterized by different partial pressures of oxygen, in microwave-induced plasmas of different power. To study the whole kinetic process the Al-metal and the oxide formed were investigated by means of a combination of grazing incidence X-ray reflectometry (GIXR) and grazing incidence X-ray diffractometry (GIXRD). XPS and FTIR spectroscopy confirmed the formation of stoichiometric Al(2)O(3). The alumina formed is X-ray amorphous. Quantitative description of oxide formation was achieved indirectly by determination of the decrease in the integrated intensity of the Al(111)-peak and the total thickness of the whole coating. These values enabled calculation of kinetic data. It was found that oxide growth was a combination of two simultaneous processes - diffusion and sputter processes. The diffusion coefficient D (cm(2) s(-1)) and the sputter rate S (nm s(-1)) were determined. The effect of the composition of the gas mixture, microwave power, and concentration of activated oxygen species on the oxidation process will be discussed. For calculation of the activation energy, E(A), of this plasma-enhanced diffusion process the temperature-dependence of D was investigated.

ELECTRICAL CHARACTERIZATION OF EPITAXIAL BI:2201

Bi2.1Sr1.9CuOy thin films (Bi:2201) were deposited onto heated single crystal (100) MgO substrates using inverted cylindrical DC magnetron sputtering with different partial pressures of oxygen in a sputtering gas. The behavior of the normal state resistivity function of temperature is strongly influenced by the composition of sputtering gas used in thin films synthesis. Near the transition to the superconducting state, electrical resistivity changes strongly from "metallic" to insulator (MI). The origin for the increase of electrical resistance was analyzed using some models for the localization of mobile carriers. A good linearity is obtained for ln R as a function of Tα for α = 1/10 and for R as a function of ln T. The last behavior agrees with the pinning and fragmentation of 1D stripes in CuO2 planes.

Preparation and characterisation of tin-doped indium oxide films

Tin-doped In2O3 (ITO) thin films were prepared by reactive evaporation from new pulverulent mixture of indium oxide, tin oxide and metallic indium at different partial pressures of oxygen. The films were annealed in a secondary vacuum just after deposition. Under optimal conditions of evaporation, these films are stoichiometric, show a good crystallinity and feature high transmission in visible region (T>90%) and high reflection in near IR region versus oxygen pressure.

Interaction of Oxygen with Nanophase Carbons Investigated by Electron Spin Resonance Spectroscopy

ABSTRACTInteraction of oxygen with three commercial activated carbons (GX203, P1400 and MEED50 supplied by PICA USA Inc., with BET surface areas of 1000, 1150 and 2000 m2/g respectively) is investigated using 9 GHz electron spin resonance (ESR) spectroscopy. All three carbons give a single ESR line with g = 2.0028(3), but the linewidth ΔH and the spin concentration Ns, are strongly affected by exposure to oxygen. The ESR parameters (g, ΔH, Ns) are measured for different partial pressures of oxygen. For the highly evacuated samples, δH ≃ 1.2 Oe and Ns≃ 1019/gm and these results are interpreted in terms of uncompensated surface dangling bonds. Oxygen exposure broadens the line and reduces Ns, in direct relation to the surface areas of the carbons and the effect is reversible. Possible effects of the paramagnetic oxygen on dangling bonds are discussed.

Structural and electrical properties of as-deposited and annealed DC sputtered ITO thin films

We have studied the effect of annealing on the structural and electrical properties of tin-doped indium oxyde, In 2 O 3 :Sn (ITO), thin films prepared by DC sputtering at different partial pressure of oxygen (ppo). Annealing experiments have been done in vacuum and in Ar atmosphere up to a temperature of 450 °C. A change of texture from (100) to (111) as the ppo was increased was noted in the as-deposited films. Annealing induced cristallinity and improved the texture of these films. The lattice constant decreased after annealing. The (222) grain size increased after vacuum annealing but was unaffected by annealing in Ar atmosphere; while the (400) grain size decreased for samples having the (100) texture. The electrical resistivity decreases sharply after annealing to a minimum value of 87 x 10 -4 Ω cm.

On the enlargement of the lattice parameter c in sputter deposited in situ prepared thin films of YBa 2Cu 3O x

The in situ growth of YBa 2Cu 3O x (123) thin films by sputtering was studied at different partial pressures of oxygen, keeping the total sputtering pressure to a constant value of 40 Pa. The grown films were characterized to investigate the previously reported increase in the lattice parameter c and the variation of the superconducting transition temperature T c with the parameter c which is found to be different from that of bulk samples. The increase in the parameter c is observed only when the films are prepared at low partial pressures of oxygen and is not dependent on the total sputtering pressure. Under these conditions, the growth promoted is non-equilibrium which facilitates the formation of an apical oxygen defect structure. For the maximum apical oxygen deficit, the c parameter is found to be 1.1815 nm. This structure has an onset superconducting transition temperature at 75K. The apical oxygen deficiency decreases on increasing the oxygen partial pressure and this fact accounts for the observed linear variation of T c with the lattice parameter c. The apical oxygen defect phasecan be gainfully used to prepare superconductor-normal-superconductor (SNS) junctions based purely on 123 material.

Pressureless sintering of Al 2O 3/SiC w materials: Effect of the reducing atmosphere

The effect of the temperature and the conditions of the reducing atmosphere on the sintering behavior of pressureless-sintered Al 2O 3/SiC w composites was studied by SEM, XRD and density measurements and analyzed throughout a thermodynamic study of the system. Different partial pressures of oxygen were estimated for two ways of arrangement of the samples, between graphite disks or packed in an SiC bed, the former being lower. A higher amount of glassy phase was observed when pressureless sintering was conducted with samples between graphite disks and at the highest sintering temperature studied (1800 °C). Taking into account the reactions that can occur at the partial oxygen pressures thermodynamically estimated, the formation of a high amount of liquid was explained throughout two mechanisms: formation of a melt with the composition of the eutectic of the Al 2O 3-Al 4C 3 binary system and liquid production by reaction of SiC and Al 2OC. The higher densities reached at 1800 °C than at 1700 °C were attributed to a liquid-phase assisted mechanism of sintering.

A comparison of conductance behaviour between SnO 2 and CdS gas-sensitive films

The conductance behaviours of SnO 2 and CdS semiconducting films as a function of temperature and after rapid changes in temperature and in oxygen partial pressure are compared. Experimental results are given at different partial pressure of oxygen in dry mixtures with nitrogen in the temperature ranges 350–850 K for SnO 2 and 300–550 K for CdS. In the case of conductance response to rapid changes in oxygen partial pressure, results are given for both an increase and a decrease of the partial pressure. Some results are also given for SnO 2 films doped with aluminium and antimony. SnO 2 samples are in the form of thick films, which together with gold electrodes are screen printed on an alumina substrate. Spray pyrolysis is used for the deposition of CdS thin films from CdCl 2 and (NH 2) 2CS solutions on glass substrates. A similar sigmoidal variation of conductance during heating is found for both SnO 2 and CdS films with a shift of 200 K and more in the temperature scale for this variation between the two films. The results are discussed in the light of conduction models where the surface barriers at intergranular contacts dominate the film resistance.

Phase Relations in the System La‐Rh‐O and Thermodynamic Properties of LaRhO3

Phase relations in the system La‐Rh‐O at 1223 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X‐ray diffraction (XRD), and energy‐dispersive analysis of X‐rays (EDAX). Only one ternary oxide, LaRhO3, with distorted orthorhombic perovskite structure (Pbnm, a = 0.5525, b= 0.5680, and c= 0.7901 nm) was identified. The alloys and intermetallics along the La‐Rh binary are in equilibrium with La2O3. The thermodynamic properties of LaRhO3 were determined in the temperature range 890 to 1310 K, using a solid‐state cell incorporating yttria‐stabilized zirconia as the electrolyte. A new four‐compartment design of the emf cell was used to enhance the accuracy of measurement. For the reaction image The compound decomposes on heating to a mixture of La2O3, Rh and O2. The calculated decomposition temperatures are 1843 (± 5) K in pure O2 and 1728 (± 5) K in air at a pressure of 1.01 × 105 Pa. The phase diagrams for the system La‐Rh‐O at different partial pressures of oxygen are calculated from the thermodynamic information.

Mathematical Modeling of Action Mechanisms of Some Aromatic Amine Class Inhibitors for Polymers

Abstract The kinetic rules of inhibited oxidation of n-hexadecane have been investigated in presence of aromatic amine inhibitors. The studies were carried out in autooxidative conditions at different rates of oxidation initiation. The study included a wide range of inhibitor concentrations and hydroperoxides at different partial pressures of oxygen. A mathematical model of the investigated process has been worked out that describes the main rules of the process and quantitatively predicts the experimental data.

Effects of oxygen tension on endothelium dependent responses in canine coronary microvessels

The aim was to determine the direct effects of oxygen tension on endothelium dependent vasodilator responses in canine coronary microvessels. Coronary microvessels were isolated and studied in vitro in a no flow constant pressure state using a video dimension analysing system. Microvessels were exposed to different partial pressures of oxygen. Endothelium dependent responses to acetylcholine and A23187 calcium ionophore were obtained with and without indomethacin during hyperoxia and normoxia, and compared to responses during hypoxia. Dose-response curves were also obtained to the direct smooth muscle dilator nitroprusside during normoxia and hypoxia. The reversibility of the effects of hypoxia on the acetylcholine response was studied after return to hyperoxic conditions following hypoxia. Coronary microvessels (58-150 micron diameter) were obtained from adult mongrel dogs of either sex. Exposure of preconstricted microvessels to hypoxia alone [PO2 5.8(0.4)kPa] resulted in a 25.9(SEM 6.8)% relaxation that was abolished by indomethacin [0.35(2.9)% relaxation]. Acetylcholine elicited dose dependent vasodilatation, with no significant differences in sensitivity between normoxia [PO2 14.6(0.04) kPa] and hypoxia: EC50 = 0.023 v 0.027 mumol.litre-1, respectively. During hyperoxia [PO2 80.2(6.0) kPa] there was a significant increase in the EC50 value to 0.09 mumol.litre-1 (hypoxia and normoxia v hyperoxia). After inhibition of prostaglandin synthesis with indomethacin, the sensitivity to acetylcholine was significantly decreased during hypoxia (EC50 = 0.16 mumol.litre-1) when compared to normoxia and hyperoxia. Indomethacin alone did not alter the acetylcholine response during normoxia and hyperoxia. As with acetylcholine, the sensitivity of indomethacin treated microvessels to A23187 was also decreased during hypoxia when compared to hyperoxia. There was no difference in the nitroprusside response during hypoxia and hyperoxia. The decreased vasodilator response to acetylcholine after hypoxia was persistent up to 2 h after return to hyperoxic conditions. Hypoxia decreases vasodilatation due to endothelium dependent relaxing factor, and oxygen tension has an important influence on both receptor dependent and receptor independent endothelium dependent vasodilator responses in coronary microvessels. Hypoxia also induces a prostaglandin mediated dilatation of preconstricted coronary microvessels. The effects of hypoxia on endothelium dependent responses are persistent up to 2 h.

Oxidation and hydrolysis kinetic studies on UN

The reaction of oxygen and water vapour with UN microspheres containing 0.78 and 10.9 mol% UO 2 as impurity was studied under non-isothermal heating conditions in a thermobalance under different partial pressures of oxygen, a fixed pressure of water vapour in argon, and in air. Uranium mononitride was ultimately converted to U 3O 8, with the formation of UO 2 and U 2N 3 as intermediates. The end product of pyrohydrolysis was UO 2. The kinetic parameters were evaluated and the mechanism of the reaction was suggested. Different kinetic models were used to explain the oxidation behaviour of UN.

Point Defects and Surface Diffusion in Iron Oxide and Nickel Oxide

Diffusion of the 57Co isotope on Fe3O4 (110) and NiO (100) surfaces was investigated by the edge‐source method. The surface diffusion parameter, αDsδ, where α is the segregation factor, Ds the surface diffusion coefficient, and δ the thickness of the high‐diffusivity layer, was determined at 750°C for different partial pressures of oxygen. In both cases point defects strongly influenced surface diffusion. For Fe3O4 the vacancy mechanism is dominant at high oxygen activities and interstitial (or interstitialcy) mechanism dominates at low oxygen activities. For NiO the surface diffusion at low oxygen activities is influenced by aliovalent impurities and at high oxygen activities the strong influence of the intrinsic defects, nickel vacancies, on surface diffusion was observed. It was concluded that similar mechanisms operate during surface diffusion in the near surface layer and during diffusion in the lattice.

The oxidative dehydrogenation of ethane by perovskite type catalysts containing oxides of strontium, cerium and ytterbium

Compounds with the general formula SrCe1−xYbxO3-0.5x have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), temperature programmed reduction (TPR) and BET, and tested for catalytic activity with respect to dehydrogenation of ethane to ethene. XRD indicates that the solubility limit of Yb2O3 in SrCeO3 is about 10 %, above which a second phase is formed. Furthermore, Yb:SrCeO3 is unstable in the presence of CO2 as it reacts to SrCO3 and Yb:CeO2. TPR measurements indicate that Ce may be reduced from tetra- to the trivalent state. BET measurements yielded specific surface areas of approximately 1m2/g. The different catalyst compositions were tested in a continuous flow tubular reactor with two different partial pressures of oxygen at 500, 600 and 700 °C. A maximum yield of 49 % was obtained at 700 °C. Possible reaction mechanisms are discussed.

A New Bessel-Box Energy Analyzer for Sputtered Neutral Mass Spectrometry

A new type energy analyzer with an electron impact ionizer for sputtered neutral mass spectrometry (SNMS), which is compact enough to be mounted in secondary ion mass spectrometry (SIMS) instruments, has been developed. The compact energy analyzer, called a modified Bessel-Box, enables energy distribution of slow charged particles with different energy resolutions to be obtained by changing the ratio of voltages applied to the analyzer. Applying this system for SNMS of Al-Mg alloy under different partial pressures of oxygen, it has been confirmed that SNMS is free from oxygen enhancement, allowing the quantification of matrix elements with considerable accuracy. It has also been revealed that the space-charge effect caused by bombarding electrons becomes fairly marked, resulting in the deformation and shift of energy distributions of the postionized particles.

Secondary ion generation mechanism studied by ISS-SIMS and work function measurements

Oxygen enhancement effects in secondary ion generation were studied in polycrystalline Ni at different partial pressures of oxygen, P o 2 , by sequential ISS-SIMS and work function measurements. The investigation has revealed that the enhancement undergoes three stages: (I) The secondary ion intensity increases monotonically with an increase of work function which is described very well by the electron tunneling model. (II) This tendency abruptly changes, i.e. the work function decreases and the secondary ion intensity increases rapidly, for a slight increase of P o 2 (III) The secondary ion intensities gradually increase and become saturated with a further increase of P o 2 . It has also been found that the critical coverage, θ c, corresponds exactly to the stage (II) behaviour, which was observed by Blaise and Bernheim for a single crystal (100)Ni surface.

Some equilibrium relationships in the barium rich part of the BaOCuOO system

The authors have examined the barium rich region of the system BaOCuOO at temperatures between 800 and 900°C in presence of gaseous atmospheres with different partial pressures of oxygen (i.e. 1; 0.21; 1.10 −6 atm). In flowing argon (pO 2 = 10 −6 atm) two new compounds corresponding to the formulae Ba 2CuO 3 and Ba 3CuO 4 have been identified, for which cell parameters and structural type were defined. In presence of pure oxygen or CO 2 free air the formation was observed instead of a phase with composition Ba 2CuO 3+δ. It can exist with two modifications characterized by a different distribution of oxygen vacancies.

A study of the temperature dependence of the barrier energy in porous tin dioxide

The dependence of conductance on temperature of some commercial and thick-film SnO 2 semiconductor gas sensors is measured in the temperature range 350 K to 875 K at different partial pressures of oxygen in nitrogen. The measurements are carried out using different heating and cooling rates. The values of the barrier enrgy between particles in the ceramic material are also calculated from these results on the basis of the single barrier model for the conductance. The value of the barrier energy in pure oxygen at a fixed temperature is first determined using the temperature-stimulated change in the conductance. The results are discussed in the light of some other experiments and theoretical models given to describe the barrier energy. A discussion on the effect of different barrier heights between different particles is also given on the basis of a random barrier network model. By using quick cooling from 875 K to 350 K, it is possible to get high barrier values also at this low temperature. It is beleived that this may be the modus operandi of temperature-pulsed sensors.