Activation Energy For Oxygen Diffusion Research Articles

Phase separation and superconductivity in La 2CuO 4+δ: Effects of oxygen diffusion

In oxygen-annealed La 2CuO 4+δ (δ ∼0.03), bulk magnetization measurements show an increase of ∼4K in the superconducting T c when the sample is cooled slowly through a narrow temperature range near 195K. At this temperature, 139La NQR spectra exhibit a concomitant appearance of an anomalous feature associated with the metallic phase whose spectral weight increases with cooling rate. The data suggests a distribution of local structures and annealing-dependent volume fraction in this part of the sample. Interpretation of these results in terms of oxygen diffusion in a phase separated material is considered and a picture consistent with the observed changes in T c is obtained. The activation energy of oxygen diffusion derived from the model, Q ∼ 0.25 eV, is in the same order of magnitude as the results obtained in La 2−xSr xCuO 4− y .

Temperature effects on permeation of modified atmosphere gas mixtures through a low density polyethylene package film

AbstractPermeation of CO2 and O2 through a low density polyethylene film was studied with CO2‐N2 mixtures in the temperature range 263‐283 K, and with CO2‐O2‐N2 mixtures in the range 257‐313 K. The temperature dependence of the permeabilities of these gases agreed with the Arrhenius expression. The activation energy for carbon dioxide diffusion was between 3.53 × 104 and 3.74 × 104J/mol; the activation energy for oxygen diffusion was 3.13 × 104J/mol. The pre‐exponential constant for oxygen was higher than that of carbon dioxide in various mixtures. It was also found that the pre‐exponential constant of carbon dioxide decreased with increasing CO2 concentration in the mixtures.

Oxygen diffusion in c-axis-oriented YBa2Cu3Ox films

C-axis-oriented YBa2Cu3O7- delta films produced by electron beam and thermal evaporation are composed of mosaic blocks. The deoxygenated YBa2Cu3Ox (x=6.1-6.2) films were annealed in an oxygen atmosphere. The change of oxygen concentration in the films during the annealing process was detected by the diffraction peak site of the (0011) peak. Applying the theory of lattice diffusion to analyse the oxygen-in-diffusion in the films, the authors obtain the activation energies for oxygen diffusion in the tetragonal and orthorhombic phases, which are 1.15 and 1.23 eV respectively. The change of shape of (00 11) diffraction peaks indicates that there is a coexistent range of two phases near the transition point. The difference between single crystals and c-axis film is that there are many mosaic boundaries in the c-axis film. A mosaic boundary acts as a short-circuit for oxygen diffusion and makes the diffusion time, during which equilibrium oxygen concentration is attained in the films, decrease greatly.

Yielding and dynamic strain aging behavior of Zircaloy-4 tube

The expanding copper mandrel test is performed at three strain rates (3.2 × 10 −5/ s, 2.0 × 10 −6/ s and 1.2 × 10 −7/ s) in the temperature range of 553–823 K by varying the heating rates in air and in vacuum. Precise measurements and exact analyses of test results are made to improve the accuracy and reliability of the expanding copper mandrel test. Yield pressures at the different strain rates and temperatures are calculated from experimental results of diametral plastic expansion and are used to determine activation parameters of yielding and dynamic strain aging. The activation energy for dynamic strain aging obtained from the yield stress peak temperatures and strain rates is 228 kj/mol and this value is in good agreement with the activation energy for oxygen diffusion in α-zirconium and Zircaloy-2 (207–220 kj/mol). Therefore, oxygen atoms are considered to be responsible for the dynamic strain aging which appears between 573 and 673 K. The expanding copper mandrel test is proved to be a convenient and quantitative testing method with simple devices for the study of yielding and strain aging behavior of thin-walled tube materials under biaxial stress conditions.

Oxygen-diffusion-limited CO formation on a Ni surface

The reaction between oxygen and carbon on a nickel film supported by a sapphire substrate has been studied with temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). Oxygen was dissolved into the nickel film from the gas phase during high-temperature oxidation and annealing. Carbon was subsequently deposited on the nickel surface from the thermal decomposition of ethylene. During TPD, the bulk oxygen diffused to the vacuum interface of the nickel film, reacted with surface carbon, and desorbed as CO. A set of CO TPD peaks obtained for increasing initial carbon coverages showed a common low-temperature leading edge. This common leading edge has been fitted to a model in which the rate-limiting step in the carbon-oxygen reaction is taken to be the diffusion of bulk oxygen to the nickel film's surface. An activation energy for oxygen diffusion in nickel of 80 kcal/mole has been obtained. Sequential carbon exposures and TPD flashes eventually resulted in bulk oxygen depletion; this manifested itself in the CO desorption spectra as a reduction in the area under the CO peak and a shift of the peak to higher temperatures.

Internal Friction and Oxygen Diffusion in <i>X</i>Na<sub>2</sub>O⋅(1-<i>X</i>)B<sub>2</sub>O<sub>3</sub>⋅2SiO<sub>2</sub> Glasses (Part 2)

In Part 1 of the present paper the internal friction of XNa2O⋅(1-X)B2O3⋅2SiO2 glasses was measured and the cause for the high-temperature peak was explained on the basis of the theory on the structure of alkali borosilicate glass proposed by Dell et al. In the present paper diffusion coefficients of oxygen in the glasses of the same composition system described above have been measured at temperatures below the glass transition points, and the mechanism for oxygen diffusion in this temperature region has been discussed by the citation of the data from literature on diffusion in glasses. The activation energies for oxygen diffusion are in good agreement with those for a mechanism for high-temperature peak observed on the internal friction curves. It is concluded that the results described above present the proof that the high-temperature peak is caused by the movement of non-bridging oxygen under stress, and that the diffusion of oxygen below the glass transition point occurs in the presence of lattice defects frozen-in at the glass transition point.

Thermogravimetric study of the recovery of oxygen-deficient superconducting YBa2Cu3O7−δ oxides in ambient oxygen

The oxides of oxygen-deficient YBa2Cu3O7−δ with δ≂0.32 in both powder and chunk form were annealed in ambient oxygen to investigate the behavior of oxygen indiffusion. Thermogravimetric measurements were used to monitor in situ weight gain during the annealing at constant heating rates between room temperature and 580 °C. The temperature for achieving a definite oxygen stoichiometry changes with the heating rates, which were varied from 0.1 to 15 °C/min. By measuring the rate dependence, the activation energy of oxygen diffusion in the powder oxide was determined to be 1.25±0.05 eV, in good agreement with the value obtained by previous resistivity measurements. However, the activation energy obtained from the chunk oxide is higher, i.e., 1.52±0.06 eV. A longer diffusion distance in the chunk oxide which requires diffusion across grains might be responsible for this discrepancy.

Oxygen diffusion in olivine: Effect of oxygen fugacity and implications for creep

Oxygen self‐diffusion experiments on single crystals of San Carlos olivine (∼Fo92) at 1200° ≤ T ≤ 1400°C, oxygen fugacities (ƒO2) along the Ni‐NiO and Fe‐FeO buffers, and silica activity at the olivine‐orthopyroxene buffer yielded results that follow the relationship D = 2.6 × 10−10 ƒO20.21±0.03 exp [−266±11 (kJ mol−1/RT)], where D is the diffusion coefficient in m2 s−1 and ƒO2 is given in pascals. The activation energy compares reasonably well with results for pure forsterite. The positive dependence of ƒO2 implies that the oxygen defect responsible for diffusion is an interstitial rather than a more sterically reasonable oxygen vacancy. Diffusion of oxygen in other close‐packed oxides has also shown a positive dependence on ƒO2. The rate of creep of single‐crystal olivine at fixed orthopyroxene activity also shows a positive ƒO2 dependence. If oxygen interstitials should be shown to be unimportant in oxygen diffusion in oxides, then coupled mechanisms such as countervacancy diffusion must be appealed to in order to explain the positive ƒO2 dependence. Such processes are rate‐limited by the diffusion of metal vacancies which also display a positive ƒO2 dependence in olivine. Compared with data for silicon diffusion in forsterite, our data indicate that oxygen is not the slowest diffusing species in olivine. The activation energy for oxygen diffusion is also low compared to that obtained in a majority of measurements of creep in single‐crystal olivine. Hence if oxygen diffusion contributes to the control of creep in olivine, it must be coupled to another process having a nonzero activation energy. A subinvestigation of the rate of sublimation from polished olivine surfaces, using a high‐resolution thermal balance, showed surface erosion rates at 1300°C of 0.13±0.10 nm/h. Such values are far too slow to noticeably affect our diffusion measurements at temperatures ≤1400°C.

Thermal recovery of oxygen-deficient superconducting YBa2Cu

We have annealed the oxygen-deficient ceramic oxide ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, where \ensuremath{\delta}=0.4, in ambient oxygen to obtain in-diffusion of oxygen. In situ resistivity measurements were used to monitor annealing at constant heating rates between room temperature and 570 \ifmmode^\circ\else\textdegree\fi{}C. The resistivity curve showed a maximum and a minimum. The temperatures where the maximum and the minimum were observed change with heating rate. By measuring their dependence on heating rate, which was varied from 15 to 0.1 \ifmmode^\circ\else\textdegree\fi{}C/min, we have determined the activation energy of oxygen diffusion in the oxide (\ensuremath{\delta}=0) to be 1.35\ifmmode\pm\else\textpm\fi{}0.10 eV. The in-diffusion is limited by a near-surface layer which requires the measured activation energy for oxygen to diffuse through it.

Contrasting oxygen diffusion in nepheline, diopside and other silicates and their relevance to isotopic systematics in meteorites

Oxygen self-diffusion coefficients have been determined in natural nepheline Na 3(Na, K)[Al 4Si 4O 16] and synthetic diopside CaMg(SiO 3) 2, at one atmosphere, by monitoring the rate of 18O exchange between CO 2 gas and minerals of pre-determined grain size (10, 12.5, and 15 μm radius). Oxygen self-diffusion in nepheline between 1000° and 1300°C fits a linear Arrhenius relation of the form: D = 5.9 × 10 −9 exp[(−25.0 ± 2.5) × 10 3 cal RT ] ; and for diopside between 1150° and 1350°C: D = 6.3 exp[(−96.7 ± 5.8) × 10 3 cal RT ] . The activation energy for oxygen diffusion in nepheline is similar to that of melilite (31.9 ± 0.1 kcal/mol), but the oxygen diffusivity is lower by two orders of magnitude. The diffusion of oxygen in diopside is similar to that of nepheline at 1375°C; however, the activation energy is almost four times higher. This contrast suggests a difference in the crystal chemical and structural controls of the minerals. Both nepheline and melilite are characterized by strongly distorted alkali sites within their frameworks, which could account for their relatively low activation energies and high diffusivities. More importantly, nepheline and melilite have sheet-like structures and high anionic porosities which may provide ready migration paths for oxygen. The concentration of open space between the silicate sheets in melilite may explain the greater diffusivity of oxygen in melilite than in nepheline. Diopside, forsterite, anorthite, spinel are characterized by high activation energies (80 to 100 kcal) and are refractory with very stable bonds and low anion porosities. Furthermore, these minerals are much denser and closer packed than nepheline or melilite making it difficult for oxygen to migrate within the crystalline structure and have access to the cation-oxygen bonds. Oxygen diffusion studies constrain interpretations of post-solidus oxygen exchange among minerals and may be used to explain the stable isotope systematics observed in Ca-Al rich inclusions of carbonaceous chondrites. The slow exchange and diffusion of oxygen in diopside suggests that the isotopic composition of clinopyroxenes in Ca-Al rich inclusions of carbonaceous chondrites has not changed appreciably since their incorporation into the meteorite. However, minerals such as nepheline and melilite, which readily exchange oxygen, record the isotopic composition of the last nebular gas to which they were exposed.

ChemInform Abstract: Effect of Vanadium on Oxygen Diffusivity in Niobium.

AbstractThe activation energies for oxygen diffusion, determined by couple experiments to be 176 kJ/mol for the Nb‐0.5 at.% V alloy and 194 kJ/mol for the Nb‐10 at.% V alloy, are significantly higher than the literature value for oxygen in Nb.

Effect of vanadium on oxygen diffusivity in niobium

The effect on the diffusivity of oxygen of vanadium additions to niobium was investigated by a diffusion couple technique. The addition of vanadium to niobium results in an increase of the activation energy for oxygen diffusion from 107 kJ mol −1 for oxygen in niobium to 176 ± 9 kJ mol −1 for the Nb-0.5at.%V alloy and to 194 ± 9 kJ mol −1 for the Nb-10at.%V alloy. This increase in the activation energy is attributed to the trapping of oxygen by vanadium atoms. Applying Kirchheim's trapping model and the results of internal friction measurements, trapping energies of about −64 and −49 kJ mol −1 were obtained for the Nb-0.5at.%V and the Nb-10at.%V alloys respectively.

Stress relaxation technique for thermally grown SiO2

A corona discharge technique has been utilized at 800 °C to fully relax thermal oxides grown on Si wafers. In an experiment involving two oxidation steps, the corona-relaxed oxides are shown to be equivalent to ∼1200 °C thermally grown or thermally relaxed oxides, both with respect to index of refraction and oxygen diffusion coefficient. The activation energy for oxygen diffusion through a completely relaxed thermal oxide is found to be 0.8 eV.

Analysis of damage profiles in poly(methyl methacrylate) in terms of oxygen diffusion and consumption

Profiles of photolytically induced chain scissions in poly(methyl methacrylate) (PMMA) and oxygen diffusion and solubility parameters have been used to estimate the activation energy of the chain scission process. The resulting activation energy of 19 kcal/mol, which does not include contributions from the activation energies of oxygen diffusion and solubility, suggests that the temperature-sensitive changes in photolytic scission in PMMA arise from changes in the efficiency of the cage effect.

On the Question of Oxygen Diffusion During Oxygen Related Thermal Donor Formation In Silicon.

In an attempt to decide the question whether enhanced oxygen diffusion is important for heat-treatments of silicon at ∼450ºC where thermal donors are formed we have conducted two types of experiments aimed at providing a measure of the “effective” oxygen diffusivity. First, we have extensively measured the temperature dependence of the thermal donor introduction rate for very short heat treatment times (20min). This measurement provides the thermal activation energy of TD formation. Since effects of long range diffusion and formation of large oxygen clusters are negligible for suchtimes and temperatures and, presumably, thermal donor formation at the lowest heat treatment temperatures is oxygen diffusion limited, it should be possible to interprete the obtained activation energy in terms of oxygen diffusivity. The change of the interstitialoxygen content is immeasureable for 20min heat treatment times. Therefore, the decay of the interstitial oxygen content was measured for longer heat treatments at 450ºC (up to 500hours). The two experiments are complementary in several ways: In one experiment the oxygen diffusion activation energy is extracted, while the other measurement provides the value of the diffusion coefficient at a given temperature. In one case thermal donors are monitored for short heat treatment times while in the other experiment the interstitial oxygen content is measured for long heat treatment times. The present measurements are different from other diffusion experiments in this temperature range where theatomic jump of isolated oxygen is monitored [1]. Here we attempt to extract an effective oxygen diffusivity under conditions of thermal donor formation since the thermal donor formation process itself might be the cause of an enhanced oxygen diffusivity.

Preparation effects on the UV optical properties of GeO2 glasses

The fusion temperature (Tφ), the oxygen partial pressure (PO2) during melting and the quenching rate from Tφ all influence the optical absorption in the 5.06-eV (245-nm) region. These observations are consistent with the assumption that the defect responsible for the optical absorption is an oxygen vacancy or complex of vacancies. The activation energy for the formation of the defect in GeO2 glasses which is repsonsible for the optical absorption is 2.3 eV which is larger than the activation energy for oxygen diffusion (∼1 eV).

Low-temperature oxygen diffusion in alpha titanium characterized by Auger sputter profiling

Anodic TiO2 films were grown on titanium foils under galvanostatic conditions at 20 mA/cm2 in an aqueous saturated solution of ammonium tetraborate. The samples were then heat treated at temperatures between 450 and 550 °C and changes in the profile of oxygen concentration as a function of depth were monitored using Auger electron spectroscopy (AES). The oxygen diffusivities were calculated from the Boltzmann–Matano method and compared with those obtained using an analytical solution to Fick’s second law. The activation energy for oxygen diffusion in this temperature range was then calculated to be 28 kcal/mol.

A saturable-trap analysis of solute segregation applied to oxygen trapping in neutron-irradiated vanadium

The activation energy for the 0.2 T m resistivity annealing stage in neutron-irradiated vanadium containing 61 wt ppm oxygen was determined to be (1.21 ± 0.06) eV. This value is reasonably close to the oxygen diffusion activation energy in vanadium of 1.26–1.28 eV. Thus, an extrinsic mechanism for the 0.2 T m annealing stage is indicated, involving oxygen migration and trapping at radiation-produced defect clusters. A simple saturable trap model for the trapping of interstitial impurity atoms at radiation-produced defect clusters is described. The model is applied to the isothermal annealing curves for vanadium containing oxygen. A good fit to the shape of the annealing curves is obtained and approximate agreement to the measured activation energy is found. However, the model appears to overestimate the amount of oxygen participating in the trapping process.

Thermal Oxidation of Sputtered Tantalum Thin Films between 100° and 525°C

Results are presented for the thermal oxidation behavior of four types of sputtered tantalum films between 100° and 525°C. These films are bcc tantalum, β-tantalum, a porous β-tantalum, and tantalum nitride (Ta2N). All four types of films show parabolic oxidation kinetics and the formation of adherent Ta2O5 (tantalum oxy-nitride for Ta2N films) with bright interference colors. The first three types of films dissolve about 12 at.% oxygen, which is much higher than the oxygen solubility found in bulk tantalum, and the films show a different degree of suboxide formation than bulk tantalum. The activation energies for oxygen diffusion in the metal and for oxide growth are 1.2 and 1.4 eV, respectively. The dielectric properties of the thermal oxide are discussed in terms of the defects in the oxide.

Effect of Composition on the Heat-treatment Time for Phase-Separating Borosilicate Glasses and the Time for Leaching the Separated Glasses

Some borosilicate glasses having limited compositions will be separated, by the heat treatment in the transformation range, into two glass-phases. One of them is acid-soluble B2O3⋅Na2O phase and the other is acid-insoluble SiO2 phase. When the segregated glass is acid treated, B2O3⋅Na2O phase is leached out leaving SiO2 rich porous glass without any destruction of original shape. This porous glass shrinks about 30% in volume by firing between 900°C and 1200°C, turning into 94-98% SiO2 glass having quartz glass-like properties.Object of this study is to clarify the relation between glass compositions and treatments of original borosilicate glass to make the above-mentioned porous glass.Experimental results were summarized as follows:(1) Minimum time required for phase-separation, t, were measured for various glasses at various temperatures. For every glasses, liner relation exists between log t and the reciprocal of the absolute temperature of heat treatment.The required time for phase-separation change with glass composition about ten times, however log t-1/T relation for various compositions showed identical gradients, and the apparent activation energy of phase-separation calculated from these results was 62kcal/mol. These values correspond to activation energy of oxygen diffusion in glasses.Linearity was found between log t (at 500°C) and Na2O/B2O3 mole ratio of these glasses.(2) The leaching rate by 1 N-H2SO4 of B2O3⋅Na2O phase of sufficiently segregated glasses were measured at 100°C, 80°C and 60°C. It was found that the rate changes about ten times depending on SiO2 content and Na2O/B2O3 mole ratio, and this will be explained in terms of difference of diameter of pores in SiO2 membrane for each glass.Linear relation between the thickness of leached layer, δM*, and square root of leaching time, √t, was found for every glass examined. Plotting of log δM* √t versus 1/T for various compositions gave straight lines of nearly same slopes, from which activation energies of leaching in the range 6.5-6.8kcal/mol were obtained.From these results, it is concluded that, as far as sufficiently segregated glass is concerned, the rate controlling process of leaching may arise from the diffusion of B2O3⋅Na2O through porous SiO2 membrane filled by the acid.Anothr linear relation was found between log δM*/√t-SiO2 content as well as between log δM*√t-Na2O2/B2O3 mole ratio.