Oxygen Diffusion Profiles Research Articles

Oxygen and cation diffusion in YBCO coated conductors

Biaxially textured YBa 2Cu 3O x (YBCO) films 0.3 μm thick were deposited on single-crystal LaAlO 3 and buffered Hastelloy C276 substrates. After annealing in 18O at 400 °C, secondary-ion mass spectrometry was used to determine oxygen-diffusion profiles and several cation-diffusion profiles within the various layers of the conductors. Oxygenation in the YBCO/LaAlO 3 specimen was relatively slow and hours would be required for full oxygenation of the YBCO. Oxygen diffusion was rapid in the coated conductor. It was dominated by diffusion along a– b planes and full oxygenation of a 0.3-μm-thick YBCO layer was achieved in several minutes. Cation interdiffusion was limited in the YBCO/LaAlO 3 specimen, but was significant within the coated conductor. Although Cu diffused out of the superconductor, an SrTiO 3 layer between textured MgO and YBCO limited diffusion of cations from the various substrate layers into the superconductor.

Oxygen Transport at the LaMnO3 Film/Yttria-Stabilized Zirconia Interface under Different Cathodic Overpotentials by Secondary Ion Mass Spectrometry

Oxygen transport under different cathodic overpotentials was investigated at the stabilized interface. A stable isotope oxygen was adopted as a diffusion marker at 1073 K under cathodic polarization, and the quenched samples were analyzed by secondary ion mass spectrometry. The diffusion profiles indicate the higher diffusivity of in film with the higher cathodic overpotentials. The introduction of oxygen vacancies by the cathodic polarization can change the diffusion profiles of in the film. The diffusion profiles of oxygen in film under the cathodic polarization were calculated from the literature data of oxygen content in as a first estimation. The calculated diffusion profiles showed a similar trend with the measured ones, but different concentration in the film under the higher polarization. © 2001 The Electrochemical Society. All rights reserved.

Oxygen transport at the interface of La 0.92MnO 3− x film/Y 0.15Zr 0.85O 1.925 single crystal

Oxygen transport was investigated at the interface of A-site deficient La 0.92MnO 3− x film/Y 0.15Zr 0.85O 1.925 single crystal at 1073 K. Isotope oxygen exchange ( 16O/ 18O exchange) and secondary ion mass spectrometry analysis (SIMS analysis) were adopted to measure the oxygen diffusion profiles at the interface. It has been found that the as-deposited film, without heat treatment, exhibited a higher diffusivity than the La 0.92MnO 3 bulk, and its interface with Y 0.15Zr 0.85O 1.925 single crystal acted as an oxide-ion blocking layer. Annealing at a temperature of 1273–1373 K made a contact between La 0.92MnO 3− x film and Y 0.15Zr 0.85O 1.925 single crystal with many small spots, which were the pathways of oxygen diffusion. Annealing above 1473 K, a significant interdiffusion of cations and morphological change occurred at the interface. Although the oxygen diffusivity decreased in the La 0.92MnO 3− x film, smooth diffusion profiles were observed at the interface of La 0.92MnO 3− x film/Y 0.15Zr 0.85O 1.925 single crystal.

Analysis of the oxygen impurity atoms beneath the surface of Cz-silicon by CPAA

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon, nitrogen and oxygen at trace levels in materials. By comparison with other techniques such as Fourier transform infrared spectroscopy (FTIR), the major advantage of the CPAA is its ability to determine the total concentration of impurities (interstitial, substitutional or incorporated in a complex). Errors due to matrix effects and surface contamination are eliminated. However, this technique does not allow analysis in the first micrometers beneath the surface because the chemical etching, required to rid the surface of superficial contaminants, removes this important part of the compounds’ active zone. The aim of this study is to solve this problem and as a result to be able to determine impurities in the vicinity of the surface. An application on oxygen diffusion profiles in Cz-silicon submitted to a rapid thermal annealing (RTA) will be discussed.

Ｍｇ‐Ｆｅ‐Ａｌ‐Ｏ系スピネル固溶体単結晶中の酸素拡散に対する酸化‐還元過程の影響

Oxide ion diffusivities were evaluated in single crystals of Mg-Al-Fe-O spinel solid solutions. The single crystals were grown by a traveling solvent floating zone technique. The diffusion coefficients of oxide ions were obtained by means of a solid-gas exchange method, using 18O isotope as tracer. The secondary mass spectrometer was used to measured the oxygen diffusion profiles in solids. Some profiles was not able to be interpreted by a simple error function. These anomalies are considered to be due to oxidizing or reducing process in the single crystals during the oxygen diffusion annealing. Iron ions preferentially diffused to surface during oxygen diffusion annealing in Mg0.93Al1.24Fe0.83O4+δ-crystals, while Mg0.91Al0.72Fe1.37O4+δ-crystals have not these behaviors. The resultant diffusion coefficient of Mg0.91Al0.72Fe1.37O4+δ-crystals were divided two temperature dependence as follows;D=2.0×10-1exp(-372(kJ/mol)/RT)cm2⋅s-1>1530KD=1.0×10-7exp(-181(kJ/mol)/RT)cm2⋅s-1<1530KThis tendency agreed with the polycrystalline data. In these samples it is considered that the oxide ions diffuses through oxygen vacancies.

The reduction half cell in biomaterials corrosion: Oxygen diffusion profiles near and cell response to polarized titanium surfaces

Mechanically assisted corrosion processes can greatly increase the oxidation currents generated in passivating alloy systems like Co-Cr and titanium due to oxide film disruption. When oxide films are abraded, repassivation and ionic dissolution both occur at rates that are orders of magnitude higher than undisrupted surfaces. The excess electrons generated by these anodic processes must be consumed in corresponding reduction reactions that include the reduction of oxygen. If large enough, these reduction reactions may locally deplete the concentration of solution-dissolved oxygen and, in turn, affect cell behavior in the vicinity of the implant surface. To date, this hypothesis has not been tested. In the present study, a scanning electrochemical microscope was used to measure oxygen concentration profiles in vitro near a planar titanium electrode polarized to different voltages representative of those attainable by titanium undergoing mechanically assisted corrosion. The potentials investigated ranged from 0 mV to -1000 mV (AgCl). The oxygen concentration as a function of distance from the titanium surface was measured using a platinum-iridium microelectrode and an amperometric technique. Also, preliminary experiments were performed to assess the response of rat calvarial osteoblast-rich cells cultured for 2 h on titanium samples polarized to two different potentials (0 mV and -1000 mV versus AgCl). The results of this study indicate that oxygen concentrations near titanium surfaces are affected by sample potentials out to probe-sample distances as great as 500 microm. Within 2 microm of the surface, oxygen concentrations decreased by 15 to 25% for sample potentials between -100 and -500 mV. At potentials more negative than -600 mV, the oxygen concentration dropped rapidly to near zero by -900 mV. The cell experiments showed a statistically significant difference in the amount of cell spreading, as measured by projected cell area, between the two groups (p < 0.03), with the cells cultured at -1000 mV undergoing much less spreading. This implies that -1000 mV inhibits normal cell behavior at the titanium surface and that this is most likely due, at least in part, to a diminished oxygen supply.

The reduction half cell in biomaterials corrosion: Oxygen diffusion profiles near and cell response to polarized titanium surfaces

The reduction half cell in biomaterials corrosion: Oxygen diffusion profiles near and cell response to polarized titanium surfaces

Oxygen diffusion in ion-implanted layer of Nb-doped SrTiO 3

Oxygen diffusion phenomena were investigated on Nb-doped SrTiO 3 crystals after Ar or F ion implantation. SIMS measurements indicated that oxygen diffusion profiles consisted of high and low diffusivity regions; the profiles were analyzed by a two-layer model and diffusion coefficients were evaluated. According to TEM observation, there existed three layers in the implanted region whose boundaries were in good agreement with the positions analyzed. A large number of dislocations were produced by the ion implantation, which disappeared upon thermal annealing. The distribution of oxygen vacancies was determined from the diffusion coefficients, and compared with the results of TRIM simulations.

Grain Boundary Phenomena in ZnO Varistors

ABSTRACTThe paper resumes essential grain boundary phenomena which were found experimentally by microcontact measurements on adjacent grains. The results suggest a ZnO homojunction model. Calculations of defect equilibria in the Schottky defect model show that homojunctions can be formed during the cooling period under the influence of an extrinsic donor species by a shift of the bulk defect equilibrium and intersecting diffusion profiles of oxygen- and zinc vacancies near the grain boundary.Recent experiments indicate that heterogeneous Bi2O3-segregation layers with a dissolved zinc-antimony-oxide compound are transformed to ZnO epitaxial layers plus a fine grained pyrochlore phase of zinc-bismuth-antimony oxide during the cooling period. Thus epitaxial ZnO layers eliminate thin Bi2O3-films and form homogeneous connections of adjacent grains.

Influence of oxygen diffusion profiles on the surface barrier of superconducting niobium

Surface irreversibility of superconducting niobium is drastically reduced by oxidation. This phenomenon is not caused by the oxide layer on the surface, but by the adjacent diffusion layer. A new method is developed to measure the oxygen profile in thin diffusion layers; the values of the diffusion coefficient are in agreement with those obtained from internal friction measurements. It is demonstrated that for a significant reduction of the irreversibility the diffusion depth should be at least of the order of the effective magnetic penetration depth. An explanation of the effect is given on the basis of the Bean-Livingston model. It is essentially due to the decrease of H c 1 in the diffusion layer.

A method to reveal depth distributions of carbon, oxygen and nitrogen in metal surfaces by means of neutron spectrometry

A method has been developed to reveal the depth distributions of the light elements carbon, nitrogen and oxygen in heavy matrices. For this purpose steel and zircaloy samples have been irradiated with deuterons and the neutron groups emitted in (d,n) reactions with the different light nuclei have been recorded using time-of-flight technique. The method has been applied to the study of steel samples that feature inhomogeneous carbon and nitrogen distributions and also to the measurement of diffusion profiles of oxygen in zirconium. With the present technique depth ranges of 10–15 μm can be analysed if the deuteron energy is chosen between 2.5 MeV and 3.5 MeV. The depth resolution improves with particle penetration from being of the order of 1–2 μm at the surface to 0.5 μm at greater depths under optimum conditions. The detection limit of the light element improves with the atomic number of the matrix and the analysed depth. For oxygen in zirconium and carbon in steel the limit of detection is of the order of 100 ppm at a depth of 10 μm. Limitations in the analysable range of the different profiles due to interfering neutron groups are discussed. The method is particularly useful for the study of oxygen profiles.

Measurement of 18O concentration profiles using resonant nuclear reactions

A convolution procedure is described for the determination of 18O diffusion profiles from data taken using the nuclear reaction 18O(p, α)15N. A Van de Graaff generator is used as a source of protons.Three types of concentration profile for the reacting species are considered: a step function, an error function and a thin-film-diffusion function. These are convoluted with functions that represent the spread and straggling of the proton beam, and the shape of the resonance capture cross section. The fit with the measured curve of resonant alpha yield against proton energy is estimated by a x2 analysis. The concentration profile parameters are varied so as to minimize x2.The analysis has proved successful in measuring oxide thicknesses on chromium and oxygen diffusion profiles in TiO2 and Cr2O3, and sample experiments are described.