Glancing angle x-ray study of the effect of oxygen on interface reactions in Al/Ni bilayers

1991 ◽  
Vol 6 (5) ◽  
pp. 935-942 ◽  
Author(s):  
S.M. Heald ◽  
E.V. Barrera
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Diffusion Path ◽  
Initial Reaction ◽  
X Ray ◽  
Interface Reactions ◽  
Glancing Angle ◽  
Effect Of Oxygen ◽  
Oxygen Impurities

Glancing angle x-ray reflectivity and EXAFS measurements have been made on a series of UHV prepared Al/Ni bilayers with varying amounts of oxygen impurities. These samples show an intrinsic reacted region prior to annealing, and for clean samples further reaction occurs at 250 °C. Oxygen is found to influence strongly the course of the reaction with an effect which depends on its location. A few percent O impurity within the Al film strongly suppresses the grain boundary diffusion path, which allows the growth of a smooth NiAl3 layer. Interfacial O exposures of 60 and 600 Langmuir both inhibit the initial reaction and raise the temperature at which further reaction occurs to as much as 300 °C with an effect which depends on exposure. The thickness of the intrinsic reaction zone is about 60 Å for clean samples, and is nearly eliminated for contaminated interfaces. The results indicate that surface/interface, grain boundary, and bulk diffusion all play important roles in the formation of these interfaces, and that each of these is influenced by O impurities.

scholarly journals Dilatometry of ball milled nickel nano powder during non-isothermal sintering

2007 ◽  
Vol 39 (1) ◽  
pp. 25-29 ◽  
Author(s):  
B.B. Panigrahi ◽  
K. Das ◽  
M.M. Godkhindi
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Sintered Density ◽  
Boundary Diffusion ◽  
Lattice Diffusion ◽  
Interface Reactions ◽  
Nano Powder ◽  
Nonisothermal Heating ◽  
Sintering Mechanisms ◽  
Diffusion Mechanisms

This work attempts to evaluate the sintering mechanisms of ball milled nanocrystalline nickel during nonisothermal heating. Samples showed a sintered density of 91.2% (theoretical) and grain growth up to 414 nm at 1273K. The activation energies of 12.4, 32.0 and 51.6 kJ/mol were found for viscous flow, lattice diffusion and grain boundary diffusion mechanisms respectively. Sintering was found to be controlled by interface reactions involving surface and grain boundary diffusions.

scholarly journals Grain boundary diffusion and its relation to segregation of multiple elements in yttrium aluminum garnet

2020 ◽  
Vol 32 (6) ◽  
pp. 675-696
Author(s):  
Joana Polednia ◽  
Ralf Dohmen ◽  
Katharina Marquardt
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Yttrium Aluminum Garnet ◽  
Bulk Diffusion ◽  
Element Distribution ◽  
Grain Boundary Diffusion ◽  
Yttrium Aluminum ◽  
Detectable Concentration ◽  
Thin Film Diffusion ◽  
Strong Segregation

Abstract. We studied grain boundary diffusion and segregation of La, Fe, Mg, and Ti in a crystallographically defined grain boundary in yttrium aluminum garnet (YAG). Bi-crystals were synthesized by wafer bonding. Perpendicular to the grain boundary, a thin-film diffusion source of a La3.60Al4.40O12 was deposited by pulsed laser deposition. Diffusion anneals were performed at 1000 and 1450 ∘C. Via a gas phase small amounts of elements were added during the experiment. The element concentration distributions in our bi-crystals were mapped using analytical transmission electron microscopy (ATEM). Our results show strong segregation of La and Ti at the grain boundary. However, in the presence of Ti, the La concentrations dropped below the detection limit. Quantitative element distribution profiles along and across the grain boundary were fitted by a numerical diffusion model for our bi-crystal geometry that considers the segregation of elements into the grain boundary. The shape of the diffusion profiles of Fe requires the presence of two diffusion modes, e.g., the co-diffusion of Fe2+ as well as Fe3+. The absence of a detectable concentration gradient along the grain boundary in many experiments allows a minimum value to be determined for the product of sDgb. The resulting sDgb are a minimum of 7 orders of magnitude larger than their respective volume diffusion coefficient, specifically for La = 10−14 m2 s−1, Fe = 10−11 m2 s−1, Mg = Si = 10−12 m2 s−1, and Ti = 10−14 m2 s−1 at 1450 ∘C. Additionally, we model the effect of convolution arising from the given spatial resolution of our analysis with the resolution of our modeled system. Such convolution effects result in a non-unique solution for the segregation coefficient, e.g., for example for Mg between 2–3. Based on our data we predict that bulk diffusion of impurities in a mono-phase polycrystalline aggregate of YAG is effectively always dominated by grain boundary diffusion.

Stress Generation during Grain Boundary Interdiffusion

2011 ◽  
Vol 309-310 ◽  
pp. 19-28 ◽  
Author(s):  
Leonid Klinger ◽  
Eugen Rabkin
Keyword(s):  
Stress Field ◽  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Concentration Distribution ◽  
Boundary Diffusion ◽  
Elastic Stress ◽  
Bulk Diffusion ◽  
Stress Generation ◽  
Additional Material ◽  
Coupled Diffusion

A grain boundary interdiffusion in a semi-infinite bicrystal under the conditions of negligible bulk diffusion is considered. We show that the inequality of intrinsic grain boundary diffusion coefficients of the two components leads to plating out of additional material at the grain boundary in the form of extra material wedge, which generates an elastic stress field in the vicinity of the grain boundary. We solved a coupled diffusion/elasticity problem and determined the time-dependent stress field and concentration distribution in the vicinity of the grain boundary.

Grain Boundary Diffusion in Co/Cu and Co/Cr Magnetic Thin Films

1993 ◽  
Vol 313 ◽  
Author(s):  
John G. Holl-Pellerin ◽  
S.G.H. Anderson ◽  
P.S. Ho ◽  
K.R. Coffey ◽  
J.K. Howard ◽  
...  
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Photoelectron Spectroscopy ◽  
Boundary Diffusion ◽  
Magnetic Thin Films ◽  
Grain Boundary Diffusion ◽  
X Ray ◽  
Before And After

ABSTRACTX-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Cu and Cr through 1000 Å thick Co films in the temperature range of 325°C to 400°C. Grain boundary diffusivities were determined by modeling the accumulation of Cu or Cr on Co surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Cu through Co is characterized by a diffusion coefficient, D0gb, of 2 × 104 cm2/sec and an activation energy, Ea,gb, of 2.4 eV. Similarly, Cr grain boundary diffusion through Co thin films occurs with a diffusion coefficient, Do,gb, of 6 × 10-2cm2/sec and an activation energy, Ea,gb of 1.8 eV. The Co film microstructure has been investigated before and after annealing by x-ray diffraction and transmission electron Microscopy. Extensive grain growth and texturing of the film occurred during annealing for Co deposited on a Cu underlayer. In contrast, the microstructure of Co deposited on a Cr underlayer remained relatively unchanged upon annealing. Magnetometer Measurements have shown that increased in-plane coercivity Hc, reduced remanence squareness S, and reduced coercive squareness S* result from grain boundary diffusion of Cu and Cr into the Co films.

Diffusion Mechanisms in Nanocrystalline and Nanolaminated Au-Cu

2007 ◽  
Vol 266 ◽  
pp. 13-28 ◽  
Author(s):  
Alan F. Jankowski
Keyword(s):  
Low Temperature ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Dominant Mechanism ◽  
Temperature Range ◽  
Diffusion Mechanisms ◽  
Kinetics Of

Thermal anneal treatments are used to identify the temperature range of the two dominant diffusion mechanisms – bulk and grain boundary. To assess the transition between mechanisms, the low temperature range for bulk diffusion is established utilizing the decay of static concentration waves in composition-modulated nanolaminates. These multilayered structures are synthesized using vapor deposition methods as thermal evaporation and magnetron sputtering. However, at low temperature the kinetics of grain-boundary diffusion are much faster than bulk diffusion. The synthesis of Au-Cu alloys (0-20 wt.% Cu) with grain sizes as small as 5 nm is accomplished using pulsed electro-deposition. Since the nanocrystalline grain structure is thermally unstable, these structures are ideal for measuring the kinetics of grain boundary diffusion as measured by coarsening of grain size with low temperature anneal treatments. A transition in the dominant mechanism for grain growth from grain boundary to bulk diffusion is found with an increase in temperature. The activation energy for bulk diffusion is found to be 1.8 eV·atom-1 whereas that for grain growth at low temperatures is only 0.2 eV·atom-1. The temperature for transitioning from the dominant mechanism of grain boundary to bulk diffusion is found to be 57% of the alloy melt temperature and is dependent on composition.

Modeling Boron Diffusion in Polycrystalline HfO2 Films

2002 ◽  
Vol 716 ◽  
Author(s):  
Chun-Li Liu
Keyword(s):  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Concentration Profiles ◽  
Boron Diffusion ◽  
Gate Stacks ◽  
Modeling Prediction ◽  
Sims Analysis

AbstractWe present ab-initio modeling results including formation, migration, and activation energies for B diffusion through bulk and grain boundaries in polycrystalline HfO2 films. Modeling results clearly indicate that B can penetrate through a 40 Å HfO2 film via grain boundary diffusion, but not by bulk diffusion. SIMS analysis of B concentration profiles for polysilicon/HfO2/Si gate stacks after different anneals showed double B peaks at the interfaces and thus confirmed the modeling prediction.

Study of Fe Diffusion in Cr2O3 by Secondary Ion Mass Spectrometry

2005 ◽  
Vol 237-240 ◽  
pp. 940-945
Author(s):  
Antônio Claret Soares Sabioni ◽  
Anne Marie Huntz ◽  
F. Silva ◽  
François Jomard
Keyword(s):  
Mass Spectrometry ◽  
Activation Energy ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Secondary Ion Mass Spectrometry ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Iron Diffusion ◽  
Ion Mass Spectrometry ◽  
Secondary Ion

Chromia protective layers are used to prevent corrosion by oxidation of many alloys, such as the stainless steels, for instance. To check if chromia is a barrier to the outward diffusion of iron in these alloys, iron diffusion in chromia was studied in both polycrystals and oxide films formed by oxidation of Ni-30Cr alloy in the temperature range 700-1100°C at an oxygen pressure equal to 10-4 atm. An iron film of about 70 nm thick was deposited on the chromia surface, and after the diffusing treatment, the iron depth profiles were established by secondary ion mass spectrometry (SIMS). Using a solution of the Fick’s second law for diffusion from a thick film, effective or bulk diffusion coefficients were determined in a first penetration domain. Then, Le Claire’s and Hart’s models allowed both the bulk diffusion coefficient and the grain boundary diffusion parameter (aDgbd) to be obtained in a second penetration domain. Iron bulk and grain boundary diffusion does not vary significantly according to the nature-microstructure of chromia. The activation energy of grain boundary diffusion is at least equal or even greater than the activation energy of bulk diffusion, probably on account of segregation phenomena. Iron diffusion was compared to cationic self-diffusion and related to the protective character of chromia.

Exafs Studies of Grain Boundary Diffusion and Segregation

1986 ◽  
Vol 77 ◽  
Author(s):  
S. M. Heald ◽  
H. Chen ◽  
J. M. Tranquada
Keyword(s):  
Thin Film ◽  
Solid State ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Structural Information ◽  
Solid State Diffusion ◽  
Interface Reactions ◽  
Tin Bronze ◽  
State Diffusion

ABSTRACTThe dominant pathway for thin film interdiffusion and interface reactions is often via grain boundaries. We have made EXAFS measurements of grain boundary constituents for two systems: interdiffusion in Ag-Au bilay-ers and solid state reaction of Nb with a copper-tin bronze to form Nb3Sn. The Ag-Au results indicate that Au in saturated Ag grain boundaries has an environment similar to a dilute Au in Ag solution with reduced coordination. For the Nb-bronze reaction, the results for the Cu environment indicate distinct changes in the grain boundary environment when small amounts of Ti, Hf, Zr, and Ta are added to the starting Nb. Both results demonstrate the ability of EXAFS to probe grain boundary environments, and to provide important structural information in understanding solid state diffusion and interdiffusion in thin film systems.

Sintering Behaviors of Pt Nanopowders with Different Particle Sizes: A Real-Time Synchrotron X-ray Scattering Study

2021 ◽  
Vol 16 (5) ◽  
pp. 849-853
Author(s):  
Jang-Hyeong Lee ◽  
Tae-Sik Cho
Keyword(s):  
Particle Size ◽  
Solid State ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Domain Size ◽  
Particle Sizes ◽  
X Ray ◽  
X Ray Scattering ◽  
Solid State Sintering

We have studied the solid state sintering behaviors of platinum (Pt) nanopowders with different particle sizes using real-time synchrotron X-ray scattering in air. Pt powders with large particle size of 101 nm at room temperature (RT) showed a defect-free crystal domain size of 10 nm. Most of these powders exhibited multiple grains inside the particle. Solid state sintering of the powders mainly occurred through surface diffusion of Pt atoms near 145 °C, grain boundary diffusion from 150 to 400 °C, and then grain growth above 550 °C. Meanwhile, Pt nanopowders with small particle size of 18 nm at RT showed a crystal domain size of 8 nm. Most of these powders exhibited a single grain inside the particle. Solid state sintering of the nanopowders mainly occurred through surface diffusion of Pt atoms near 151 °C and then grain growth above 400 °C. Grain boundary diffusion does not happen because grain boundary hardly exists.

Sr-Diffusion in Ce0.8Gd0.2O2-δ Layers for SOFC Application

2013 ◽  
Vol 1542 ◽  
Author(s):  
Tabea Mandt ◽  
Carsten Korte ◽  
Uwe Breuer ◽  
Alexander Weber ◽  
Mirko Ziegner ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Barrier Layer ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Diffusion Activation Energy ◽  
Boundary Density ◽  
Long Term Stability ◽  
Maximum Lifetime

ABSTRACTIn this study Sr2+ diffusion along Ce0.8Gd0.2O2-δ (CGO) grain boundaries is investigated. Model samples with different grain boundary densities were prepared by different thin film tech-niques. Diffusion experiments were performed by annealing and subsequent ToF-SIMS analysis. The activation energy of grain boundary diffusion is determined as 492 kJ/mol, which is 2/3 of the bulk diffusion activation energy 739 kJ/mol, deduced from literature data [1-5].The formation of an electrical blocking SrZrO3 layer due to grain boundary diffusion of Sr2+ through a CGO barrier layer may limit the long term stability of Solid Oxide Fuel Cells based on Zr0.85Y0.15O2-δ electrolytes and La0.58Sr0.4Co0.2Fe0.8O3-δ cathodes. The grain boundary diffusivity and the CGO grain boundary density highly influence the kinetic of the SrZrO3 formation. Aim of this study is to gain data for a prediction of the maximum lifetime of a SOFC system, limited by the increasing cell resistivity due to SrZrO3 formation. Specifications for the CGO barrier layer preparation concerning grain boundary density are determined.

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