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Sergiy V Divinski - One of the best experts on this subject based on the ideXlab platform.
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Tracer Diffusion in single crystalline cocrfeni and cocrfemnni high entropy alloys kinetic hints towards a low temperature phase instability of the solid solution
Scripta Materialia, 2020Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury Chumlyakov, Fabian HergemollerAbstract:Abstract Tracer-Diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the existence of a low-temperature modification of the equiatomic solid-solution phase in CoCrFeMnNi. The temperature-dependent correlation factors of all elements are determined within the framework of the random alloy model providing insights into potential mechanisms of the kinetic anomaly.
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experimental and theoretical study of Tracer Diffusion in a series of cocrfemn 100 xni alloys
Acta Materialia, 2020Co-Authors: Josua Kottke, Mathilde Laurentbrocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, łukasz Rogal, Daniel Utt, Alexander Stukowski, Karsten Albe, Sergiy V DivinskiAbstract:Abstract Tracer Diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn) 100 − x Nix alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured Tracer Diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.
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Tracer Diffusion in the ni cocrfemn system transition from a dilute solid solution to a high entropy alloy
Scripta Materialia, 2019Co-Authors: Josua Kottke, Mathilde Laurentbrocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, łukasz Rogal, Sergiy V Divinski, Gerhard WildeAbstract:Abstract Tracer Diffusion of Co, Cr, Fe and Ni is measured at 1373 K in Co20Cr20Fe20Mn20Ni20, Co10Cr10Fe10Mn10Ni60 and Co2Cr2Fe2Mn2Ni92 alloys. Diffusion retardation in the high-entropy Co20Cr20Fe20Mn20Ni20 alloy is most prominent in comparison to the Co2Cr2Fe2Mn2Ni92 solid solution, however the concept of ‘sluggish’ Diffusion cannot be used as a blanket statement. The Tracer Diffusion coefficient drops either slightly (by a factor of three, Fe) or marginally (by a factor of 1.2, Ni) if compared at 1373 K. Alternatively, if compared on a homologous temperature scale, the Diffusion retardation can be as large as a factor of 30 (Fe) or 10 (Ni).
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Tracer Diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high entropy alloys
Journal of Materials Research, 2018Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury ChumlyakovAbstract:High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, Diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally solute Diffusion of Mn in the quaternary alloy is investigated using the radioTracer technique, thereby the Tracer Diffusion coefficients of ^57Co, ^51Cr, ^59Fe, ^54Mn, and ^63Ni are determined at a temperature of 1373 K. The components are characterized by significantly different Diffusion rates, with Mn being the fastest element and Ni and Co being the slowest ones. Furthermore, solute Diffusion of Cu in the CoCrFeNi single crystal is investigated in the temperature range of 973–1173 K using the ^64Cu isotope. In the quaternary alloy, Cu is found to be a fast diffuser at the moderate temperatures below 1273 K and its Diffusion rate follows the Arrhenius law with an activation enthalpy of about 149 kJ/mol.
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bulk Tracer Diffusion in cocrfeni and cocrfemnni high entropy alloys
Acta Materialia, 2018Co-Authors: Sergiy V Divinski, Gerhard Wilde, M Vaidya, B S Murty, Konda Gokuldoss PradeepAbstract:Abstract High entropy alloys (HEAs) have emerged as a promising class of equiatomic or near equiatomic multicomponent alloys, which garner fundamental curiosities and interest in high temperature applications. Understanding Diffusion kinetics of HEAs is critical to assess their phase stability and deformation behaviour, particularly at elevated temperatures. For the first time, bulk Tracer Diffusion coefficients of Co, Cr, Fe and Mn are determined in polycrystalline CoCrFeNi and CoCrFeMnNi HEAs using the radioTracer method in the temperature interval of 1073–1373 K. Material homogeneity and the absence of any phase decomposition in CoCrFeNi and CoCrFeMnNi HEAs were established by electron microscopy and atom probe tomography investigations. Both bulk and grain boundary Diffusion contributions to penetration profiles are observed for Diffusion of Co, Cr, Fe and Mn Tracers in both HEAs. The temperature dependencies of bulk Diffusion for all Tracers show Arrhenius behaviour. The corresponding activation energies (Q) and the logarithm of pre-exponential factors (D0) show a linear relationship, thus following the “compensation rule”. An increase of the configurational entropy leads to reduced Diffusion rates only when a homologous temperature scale is used for comparison. The increase of activation energy barrier and lower frequency factors both contribute to the decreased Diffusion rates. A cross-over temperature (Tc = 1020 K) is observed for Co Diffusion (on slight extrapolation of Arrhenius plot) in CoCrFeNi and CoCrFeMnNi HEAs, while Cr and Fe exhibit almost parallel Arrhenius lines. Above Tc, the Co diffusivity is higher in CoCrFeMnNi than in CoCrFeNi, which suggests that Diffusion in HEAs need not be assumed to retard with an increasing number of elements. The existence of a cross-over temperature correlates with the change in binding energy (or enthalpy) of the constituents from CoCrFeNi to CoCrFeMnNi.
J A Kilner - One of the best experts on this subject based on the ideXlab platform.
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oxygen Tracer Diffusion and surface exchange kinetics in ba0 5sr0 5co0 8fe0 2o3 δ
Solid State Ionics, 2014Co-Authors: A Berenov, J A Kilner, A Atkinson, M V Ananyev, V A Eremin, N M Porotnikova, A S Farlenkov, E Kurumchin, Henricus J M Bouwmeester, Edith BucherAbstract:The oxygen Tracer Diffusion coefficient, Db⁎, and the oxygen Tracer surface exchange coefficient, k, were measured in Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF5582) over the temperature range of 310–800 °C and the oxygen partial pressure range of 1.3 × 10−3–0.21 bar. Several measurement techniques were used: isotope exchange followed by depth profiling (IEDP) within individual single grains or line scanning (IELS) along the sample cross-section and gas-phase analysis (GPA). Surface exchange kinetics was initially found to be slow and presumably inhibited by the formation of a passivating layer on the sample surface. High temperature pre-anneals (900–950 °C) changed the nature of this layer and enhanced surface exchange. Fast bulk oxygen Diffusion and surface exchange kinetics were observed after high temperature pre-anneals within the temperature range studied. The activation energies for 18O Tracer Diffusion and surface exchange at 0.21 bar were 0.72 ± 0.05 and 1.10 ± 0.15 eV, respectively. The Tracer Diffusion coefficient showed weak dependence upon oxygen partial pressure, whereas the surface exchange coefficient exhibited strong oxygen partial pressure dependence. The microstructure of the samples (the porosity and grain size) had a profound effect on the measured Tracer Diffusion coefficient.
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determination of proton and oxide ion Tracer Diffusion in lanthanum tungstate la w 5 6 by means of tof sims
Physical Chemistry Chemical Physics, 2012Co-Authors: Ragnhild Hancke, J A Kilner, Sarah Fearn, Reidar HaugsrudAbstract:Tracer Diffusion of protons and oxide ions, as well as chemical Diffusion of water, have been determined for the high temperature proton conductor lanthanum tungstate by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). The oxygen Tracer Diffusion and surface exchange coefficients, and , were measured after exchange anneals in water vapor enriched in H218O between 350 and 620 °C, and the apparent activation energies were 176 and 82 kJ mol−1, respectively. The hydrogen Tracer Diffusion coefficient () was measured between 220 and 320 °C after exchange anneals in D2O-containing atmospheres, and the apparent activation energy was 63 kJ mol−1. The extracted agrees with the results of transient conductivity- and TG-measurements. Chemical Diffusion and surface exchange coefficients, and , were measured at 250 and 400 °C, and the result confirms that the material is hydrated by ambipolar sluggish transport of protons and oxide ions. The surface exchange coefficients were compared to the result of TG relaxation, suggesting that access to oxygen vacancies limits the overall surface exchange reaction under incorporation of water and oxygen.
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oxygen Tracer Diffusion and surface exchange kinetics in la0 6sr0 4coo3 δ
Solid State Ionics, 2010Co-Authors: A Berenov, J A Kilner, A Atkinson, Edith Bucher, Werner SitteAbstract:Abstract The oxygen Tracer Diffusion coefficient, D*, and the oxygen Tracer surface exchange coefficient, k*, were measured in La0.6Sr0.4CoO3 − δ over the temperature range of 406–680 °C and the oxygen partial pressure range 0.044–1.019 bar. Distortions of the near surface regions of the Diffusion profiles were observed in several specimens. 18O exchange experiments were modeled by the Finite Element method and the origin of the observed distortions was assigned to exchange of oxygen during sample cooling. The estimated error in the determination of D* and k* was found to be less than 20%. The activation energies of D* and k* were 1.84 ± 0.02 eV and 0.76 ± 0.13 eV, respectively. D* was found to decrease with oxygen partial pressure following the power law with a power of − 0.55 ± 0.10. The effect of Sr doping on the values of D* in Ln1 − xSrxCoO3 − δ (Ln = La, Sm) perovskites is discussed. The data obtained from isotopic exchange measurements at 500–600 °C are in good agreement with the kinetic parameters derived from conductivity relaxation experiments on samples from the same batch.
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anisotropic oxygen Diffusion properties in epitaxial thin films of la2nio4 δ
Journal of Materials Chemistry, 2008Co-Authors: Monica Burriel, J A Kilner, G Garcia, Jose Santiso, R J Chater, Stephen J SkinnerAbstract:We report on the development and validation of a new methodology for the determination of anisotropic Tracer Diffusion and surface exchange coefficients of high quality epitaxial thin films in the two perpendicular directions (transverse and longitudinal), by the isotopic exchange technique. Measurements were performed on c-axis oriented La2NiO4+δ films grown on SrTiO3 (100) and NdGaO3 (110) by pulsed injection metal organic chemical vapour deposition (PIMOCVD), with different thicknesses ranging from 33 to 370 nm. The effect that the strain induced by the film–substrate mismatch has on the oxygen Diffusion through the film was evaluated. Both Tracer Diffusion coefficients, along the c-axis and along the ab plane, were found to increase with film thickness, i.e., as the stress of the film decreases, while the thickness seems to have no effect on the Tracer surface exchange coefficient. Best fits were obtained when considering the thickest films composed by two regions with different c-axis Tracer Diffusion coefficient values, a higher and constant D* close to the film surface and a variable decreasing D* closer to the substrate. As expected, the Tracer Diffusion and surface exchange coefficients are thermally activated and are approximately two orders of magnitude higher along the ab plane than along the c-axis. The low activation energies of D* compared with bulk values for both directions at low temperatures seem to confirm the contribution of a vacancy mechanism to the ionic conduction.
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a sims study of oxygen Tracer Diffusion and surface exchange in la0 8sr0 2mno3 δ
Materials Letters, 2000Co-Authors: R A De Souza, J A Kilner, J F WalkerAbstract:Abstract The 18 O/ 16 O isotope exchange/depth profile (IEDP) method has been employed to investigate oxygen Tracer Diffusion and surface exchange behaviour in the perovskite oxide La 0.8 Sr 0.2 MnO 3+ δ at temperatures between 700°C and 1000°C. The activation enthalpy for oxygen Tracer Diffusion in the bulk ( D b *) was found to be 270±13 kJ mol −1 , while that for oxygen Tracer surface exchange ( k s *) was 128±21 kJ mol −1 . Evidence of short circuit Diffusion was observed in all 18 O penetration profiles, and this was ascribed to fast Diffusion down grain boundaries. D b * and k s * were also determined as a function of oxygen partial pressure at 1000°C: D b *was found to vary according to P O 2 −0.41 ; the P O 2 dependence of k s *was unclear, as the 18 O penetration profiles at 1000°C were Diffusion-limited.
Gerhard Wilde - One of the best experts on this subject based on the ideXlab platform.
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Tracer Diffusion in single crystalline cocrfeni and cocrfemnni high entropy alloys kinetic hints towards a low temperature phase instability of the solid solution
Scripta Materialia, 2020Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury Chumlyakov, Fabian HergemollerAbstract:Abstract Tracer-Diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the existence of a low-temperature modification of the equiatomic solid-solution phase in CoCrFeMnNi. The temperature-dependent correlation factors of all elements are determined within the framework of the random alloy model providing insights into potential mechanisms of the kinetic anomaly.
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Tracer Diffusion in the ni cocrfemn system transition from a dilute solid solution to a high entropy alloy
Scripta Materialia, 2019Co-Authors: Josua Kottke, Mathilde Laurentbrocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, łukasz Rogal, Sergiy V Divinski, Gerhard WildeAbstract:Abstract Tracer Diffusion of Co, Cr, Fe and Ni is measured at 1373 K in Co20Cr20Fe20Mn20Ni20, Co10Cr10Fe10Mn10Ni60 and Co2Cr2Fe2Mn2Ni92 alloys. Diffusion retardation in the high-entropy Co20Cr20Fe20Mn20Ni20 alloy is most prominent in comparison to the Co2Cr2Fe2Mn2Ni92 solid solution, however the concept of ‘sluggish’ Diffusion cannot be used as a blanket statement. The Tracer Diffusion coefficient drops either slightly (by a factor of three, Fe) or marginally (by a factor of 1.2, Ni) if compared at 1373 K. Alternatively, if compared on a homologous temperature scale, the Diffusion retardation can be as large as a factor of 30 (Fe) or 10 (Ni).
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Tracer Diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high entropy alloys
Journal of Materials Research, 2018Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury ChumlyakovAbstract:High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, Diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally solute Diffusion of Mn in the quaternary alloy is investigated using the radioTracer technique, thereby the Tracer Diffusion coefficients of ^57Co, ^51Cr, ^59Fe, ^54Mn, and ^63Ni are determined at a temperature of 1373 K. The components are characterized by significantly different Diffusion rates, with Mn being the fastest element and Ni and Co being the slowest ones. Furthermore, solute Diffusion of Cu in the CoCrFeNi single crystal is investigated in the temperature range of 973–1173 K using the ^64Cu isotope. In the quaternary alloy, Cu is found to be a fast diffuser at the moderate temperatures below 1273 K and its Diffusion rate follows the Arrhenius law with an activation enthalpy of about 149 kJ/mol.
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bulk Tracer Diffusion in cocrfeni and cocrfemnni high entropy alloys
Acta Materialia, 2018Co-Authors: Sergiy V Divinski, Gerhard Wilde, M Vaidya, B S Murty, Konda Gokuldoss PradeepAbstract:Abstract High entropy alloys (HEAs) have emerged as a promising class of equiatomic or near equiatomic multicomponent alloys, which garner fundamental curiosities and interest in high temperature applications. Understanding Diffusion kinetics of HEAs is critical to assess their phase stability and deformation behaviour, particularly at elevated temperatures. For the first time, bulk Tracer Diffusion coefficients of Co, Cr, Fe and Mn are determined in polycrystalline CoCrFeNi and CoCrFeMnNi HEAs using the radioTracer method in the temperature interval of 1073–1373 K. Material homogeneity and the absence of any phase decomposition in CoCrFeNi and CoCrFeMnNi HEAs were established by electron microscopy and atom probe tomography investigations. Both bulk and grain boundary Diffusion contributions to penetration profiles are observed for Diffusion of Co, Cr, Fe and Mn Tracers in both HEAs. The temperature dependencies of bulk Diffusion for all Tracers show Arrhenius behaviour. The corresponding activation energies (Q) and the logarithm of pre-exponential factors (D0) show a linear relationship, thus following the “compensation rule”. An increase of the configurational entropy leads to reduced Diffusion rates only when a homologous temperature scale is used for comparison. The increase of activation energy barrier and lower frequency factors both contribute to the decreased Diffusion rates. A cross-over temperature (Tc = 1020 K) is observed for Co Diffusion (on slight extrapolation of Arrhenius plot) in CoCrFeNi and CoCrFeMnNi HEAs, while Cr and Fe exhibit almost parallel Arrhenius lines. Above Tc, the Co diffusivity is higher in CoCrFeMnNi than in CoCrFeNi, which suggests that Diffusion in HEAs need not be assumed to retard with an increasing number of elements. The existence of a cross-over temperature correlates with the change in binding energy (or enthalpy) of the constituents from CoCrFeNi to CoCrFeMnNi.
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ni Tracer Diffusion in cocrfeni and cocrfemnni high entropy alloys
Journal of Alloys and Compounds, 2016Co-Authors: M Vaidya, Gerhard Wilde, Simon Trubel, B S Murty, Sergiy V DivinskiAbstract:Abstract High entropy alloys (HEAs) are multicomponent alloys in equiatomic or nearly equiatomic composition. Anticipated sluggish atomic Diffusion is reported to be one of the core effects in HEAs which is presumably responsible for their many unique properties. For the first time, in the present study, Tracer (Ni) Diffusion in CoCrFeNi and CoCrFeMnNi alloys is measured by the radioTracer technique in the temperature range of 1073–1373 K using the 63 Ni isotope. Chemically homogeneous alloys of equiatomic composition were prepared by a vacuum arc melting route. The microstructure and phase stability of the alloys in the given temperature range is confirmed by differential thermal analysis and X-ray diffraction. Ni Diffusion in both CoCrFeNi and CoCrFeMnNi alloys is found to follow Arrhenius behavior. When plotted against the homologous temperature, a tendency to a successive slow down of the Tracer Diffusion rate with an increased number of components in equiatomic alloys is unambiguously established. Both the entropy term as well as the energy barriers is revealed to contribute to this trend. The current results indicate that Diffusion in HEAs cannot a priori be considered as sluggish.
Joachim Maier - One of the best experts on this subject based on the ideXlab platform.
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oxygen Tracer Diffusion in dense ba0 5sr0 5co0 8fe0 2o3 δ films
Applied Physics Letters, 2009Co-Authors: L Wang, Joachim Maier, R Merkle, T Acarturk, U StarkeAbstract:Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) is an interesting material for high temperature oxygen permeation membranes and solid oxide fuel cell cathodes, applications for which oxygen transport properties are crucial. Here oxygen isotope exchange is performed on dense BSCF films prepared by pulsed laser deposition on MgO single crystal substrates. The oxygen isotope profile is analyzed by secondary ion mass spectrometry to extract Tracer Diffusion coefficients D∗ and effective surface exchange constants k∗. Tracer Diffusion has a low activation energy of 0.5 eV. At moderate temperatures, the related oxygen vacancy Diffusion coefficient DVO is significantly larger than that for (La,Sr)(Fe,Co)O3−δ perovskites.
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Tracer Diffusion and chemical Diffusion of oxygen in acceptor doped srtio 3
Journal of Physics and Chemistry of Solids, 2000Co-Authors: J Claus, M Leonhardt, Joachim MaierAbstract:Abstract Oxygen Tracer and oxygen chemical Diffusion coefficients have been determined for single crystalline SrTiO 3 under defined temperature ( f ), oxygen partial pressure ( p (O 2 )), and acceptor (Fe) dopant concentration ( m Fe ) conditions. Oxygen Tracer Diffusion results were obtained (873 K ≤T≤1173 K , p( O 2 )=10 5 Pa ) by means of 18 O isotope exchange with subsequent analysis of the 18 O in-Diffusion profiles by secondary ion mass spectrometry (SIMS). In the case of chemical Diffusion an in situ and spatially resolved, optical relaxation technique was applied (673 K ≤T≤973 K , 10 Pa ≤p( O 2 )≤10 5 Pa ). The dopant concentration in both experiments was varied between 4.3×10 18 cm −3 ≤m Fe ≤4.9×10 19 cm −3 . The evaluation of (ex situ) Tracer and (in situ) concentration profiles are shown to be in excellent agreement with defect chemical calculations. In contrast to the Tracer Diffusion coefficients ( D ∗ ) the chemical Diffusion coefficients ( D δ ) are sensitive to ionic–electronic (short-range) defect interactions (internal buffer effects influence the thermodynamic factor) caused by valence changes of the redox-active Fe-doping.
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oxygen Tracer Diffusion in la2 xsrxcuo4 y single crystals
Journal of the American Ceramic Society, 1993Co-Authors: Elizabeth J Opila, Joachim Maier, Harry L Tuller, B J WuenschAbstract:The Tracer Diffusion of O-18 in La(2-x)Sr(x)CuO(4-y) single crystals (x = 0 to 0.12) has been measured from 400 to 700 C in 1 atm of oxygen using SIMS analysis. Evidence for Diffusion by a vacancy mechanism was found at low strontium contents. Oxygen diffusivities for x greater than or = 0.07 were depressed by several orders of magnitude below the diffusivity for undoped La2CuO(4+/-y). The observed effects of strontium doping on oxygen diffusivity are discussed in terms of defect chemical models. The decreasing oxygen diffusivity with increasing strontium was attributed to the ordering of oxygen vacancies at large defect concentrations. A Diffusion anisotropy D(sub ab)/D(sub c) of nearly 600 was also found at 500 C.
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mass transport in the presence of internal defect reactions concept of conservative ensembles iv Tracer Diffusion and intercorrelation with chemical Diffusion and ion conductivity
Journal of the American Ceramic Society, 1993Co-Authors: Joachim MaierAbstract:The Tracer Diffusion coefficient is analyzed for the case in which internal ionization equilibria have to be considered, using the concept of conservative ensembles. The relationships of the Tracer Diffusion coefficient with other phenome-nological parameters, viz., the chemical Diffusion coefficient and the Diffusion coefficient derived from the ionic conductivity, as well as with the defect diffusivities are given. The importance of mobile partially ionized or neutral defects is highlighted. In this respect the formulation of the Tracer Diffusion as an ambipolar Diffusion of the different isotopes is helpful.
Daniel Gaertner - One of the best experts on this subject based on the ideXlab platform.
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Tracer Diffusion in single crystalline cocrfeni and cocrfemnni high entropy alloys kinetic hints towards a low temperature phase instability of the solid solution
Scripta Materialia, 2020Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury Chumlyakov, Fabian HergemollerAbstract:Abstract Tracer-Diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the existence of a low-temperature modification of the equiatomic solid-solution phase in CoCrFeMnNi. The temperature-dependent correlation factors of all elements are determined within the framework of the random alloy model providing insights into potential mechanisms of the kinetic anomaly.
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experimental and theoretical study of Tracer Diffusion in a series of cocrfemn 100 xni alloys
Acta Materialia, 2020Co-Authors: Josua Kottke, Mathilde Laurentbrocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, łukasz Rogal, Daniel Utt, Alexander Stukowski, Karsten Albe, Sergiy V DivinskiAbstract:Abstract Tracer Diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn) 100 − x Nix alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured Tracer Diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.
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Tracer Diffusion in the ni cocrfemn system transition from a dilute solid solution to a high entropy alloy
Scripta Materialia, 2019Co-Authors: Josua Kottke, Mathilde Laurentbrocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, łukasz Rogal, Sergiy V Divinski, Gerhard WildeAbstract:Abstract Tracer Diffusion of Co, Cr, Fe and Ni is measured at 1373 K in Co20Cr20Fe20Mn20Ni20, Co10Cr10Fe10Mn10Ni60 and Co2Cr2Fe2Mn2Ni92 alloys. Diffusion retardation in the high-entropy Co20Cr20Fe20Mn20Ni20 alloy is most prominent in comparison to the Co2Cr2Fe2Mn2Ni92 solid solution, however the concept of ‘sluggish’ Diffusion cannot be used as a blanket statement. The Tracer Diffusion coefficient drops either slightly (by a factor of three, Fe) or marginally (by a factor of 1.2, Ni) if compared at 1373 K. Alternatively, if compared on a homologous temperature scale, the Diffusion retardation can be as large as a factor of 30 (Fe) or 10 (Ni).
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Tracer Diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high entropy alloys
Journal of Materials Research, 2018Co-Authors: Daniel Gaertner, Josua Kottke, Sergiy V Divinski, Gerhard Wilde, Yury ChumlyakovAbstract:High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, Diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally solute Diffusion of Mn in the quaternary alloy is investigated using the radioTracer technique, thereby the Tracer Diffusion coefficients of ^57Co, ^51Cr, ^59Fe, ^54Mn, and ^63Ni are determined at a temperature of 1373 K. The components are characterized by significantly different Diffusion rates, with Mn being the fastest element and Ni and Co being the slowest ones. Furthermore, solute Diffusion of Cu in the CoCrFeNi single crystal is investigated in the temperature range of 973–1173 K using the ^64Cu isotope. In the quaternary alloy, Cu is found to be a fast diffuser at the moderate temperatures below 1273 K and its Diffusion rate follows the Arrhenius law with an activation enthalpy of about 149 kJ/mol.