Dynamics of Atomic Ordering in Bulk and Thin Film Intermetallic Alloys: A Complementary Approach to Atomic Migration

2008 ◽  
Vol 1128 ◽  
Author(s):  
Wolfgang Pfeiler ◽  
Wolfgang Püschl ◽  
Chaisak Issro ◽  
Rafal Kozubski ◽  
Veronique Pierron-Bohnes
Keyword(s):  
Structural Changes ◽  
Materials Science ◽  
Kinetic Monte Carlo ◽  
Atomic Order ◽  
Intermetallic Alloys ◽  
Technical Application ◽  
Complementary Approach ◽  
Kinetic Monte Carlo Simulations ◽  
The Stability ◽  
Degree Of Order

AbstractOne of the foremost challenges in today's materials science is the design and development of materials with physical properties customized for technical application. Due to their excellent corrosion resistance and their advantageous mechanical and in many cases also magnetic properties, intermetallic alloys are among the most important materials of the 21st century. Most of their outstanding qualities are linked to long-range order, the fact that unlike atoms are preferred as neighbours, which then segregate to different sublattices. In most intermetallics atomic order persists up to rather high temperatures, if not up to melting. However, connected with the entropy gain, the degree of order depends on temperature and thereby the stability of the designed beneficial materials properties is affected. By monitoring changes in the degree of atomic order an access to atom migration is gained, which is complementary to the usual diffusion experiments, where the degree of order is not changed on average. It is shown in this review on some selected examples how an adequate thermal treatment of the samples in combination with the experimental approach gives detailed information on atom jump mechanisms and structural changes, especially if experiment is combined with up-to-date kinetic Monte Carlo simulations.

scholarly journals Kinetic Monte Carlo Simulations of Electrochemical Oxidation and Reduction of Pt(111)

2019 ◽  
Vol 166 (16) ◽  
pp. H888-H896
Author(s):  
J. Erlebacher ◽  
J. Kubal ◽  
Z. Zeng ◽  
J. Greeley ◽  
K. Struk ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Electrochemical Oxidation ◽  
Kinetic Monte Carlo ◽  
Complex Surface ◽  
Surface Roughening ◽  
Morphological Response ◽  
Kinetic Monte Carlo Simulations ◽  
Place Exchange ◽  
The Stability

Kinetic Monte Carlo simulations of electrochemical oxidation and reduction are presented that match many features of the experimentally observed electrochemical and morphological response of Pt(111). Included in the simulation are all relevant microscopic transitions, including the formation of Pt-OH and Pt-O from Pt, surface diffusion of all three species, as well as an effective place exchange diffusion at high potential. A detailed description of this approach to modeling such a complex surface is also presented. Overall, it is found that many features of the Pt(111) CV, including hydroxylation, hysteresis, and surface roughening, can be correlated to events associated with n-coordinated surface species, such as the hydroxylation wave corresponding to a one-electron oxidation of 9-coordinated terrace sites. Oxidation to Pt-O species at potentials above 1.0 V are shown to correlate to the presence of growing surface roughness, and the simulations suggest the onset of Pt-O formation in steady-state cyclic voltammetry is dominated by the oxidation of 8-coordinated step edges rather than terrace sites. Implications for the stability of Pt(111) catalysts after thousands of voltammetric cycles are discussed.

Model for the catalytic reduction of no on a surface with species desorption and impurities that cannot desorb

2021 ◽  
Author(s):  
E. J. Hernández ◽  
G. M. Buendía
Keyword(s):  
Catalytic Reduction ◽  
Kinetic Monte Carlo ◽  
Dynamical Behavior ◽  
Square Lattice ◽  
Modified Model ◽  
Reduction Of No ◽  
Large Fluctuations ◽  
Long Time ◽  
Kinetic Monte Carlo Simulations ◽  
The Stability

The dynamical behavior of a modified Yaldram–Khan model for the catalytic reduction of NO on a surface is studied by Kinetic Monte Carlo simulations. In this modified model, temperature effects are incorporated as desorption rates of the N and CO species. How the presence of contaminants in the gas phase affects the catalytic process is also analyzed by including impurities that can be adsorbed on the lattice and once there remain inert. When N desorption is included, a reactive window appears that is not present in the original YK model on a square lattice. When CO desorption is added large fluctuations appear in the coverages, the system can take a long time to stabilize, during this period, a long lasting reactive state exists that disappears when the stability is reached. When nondesorbing impurities are added, the discontinuous transition to a CO poisoned phase that presents the original YK model disappears, the coverages become continuous, and a nonreactive steady-state is rapidly reached.

Atomistic Modeling of III-V Semiconductors: Thermodynamic Equilibrium and Growth Kinetics

2001 ◽  
Vol 701 ◽  
Author(s):  
Frank Grosse ◽  
William Barvosa-Carter ◽  
Jennifer J. Zinck ◽  
Mark F. Gyure
Keyword(s):  
Thermodynamic Equilibrium ◽  
Growth Kinetics ◽  
Density Functional ◽  
Kinetic Monte Carlo ◽  
Continuous Phase ◽  
Determining Factors ◽  
Equilibrium And Kinetics ◽  
Kinetic Monte Carlo Simulations ◽  
The Stability ◽  
Stable Reconstruction

ABSTRACTGrowth kinetics and thermodynamic equilibrium can both be determining factors at different stages of III-V semiconductor heteroepitaxy. We study their interplay, employing kinetic Monte Carlo simulations for the InAs(001) surface. The simulation contains atomistic details of both species, including the stability of different reconstructions and their kinetics. The behavior of the surface in thermodynamic equilibrium, including different reconstructions, is determined exclusively by extensive total energy calculations employing ab initio density functional theory. The continuous phase transition between the α2(2x4) and β2(2x4), predicted by theory, is confirmed by experiment. At full layer coverage, a recovery of the stable reconstruction is observed. The different time scales associated with As2 and In are discussed with respect to equilibrium and kinetics.

Atomistic Modeling of III-V Semiconductors: Thermodynamic Equilibrium and Growth Kinetics

2001 ◽  
Vol 692 ◽  
Author(s):  
Frank Grosse ◽  
William Carter-Barvosa ◽  
Jennifer J. Zinck ◽  
Mark F. Gyure
Keyword(s):  
Thermodynamic Equilibrium ◽  
Growth Kinetics ◽  
Density Functional ◽  
Kinetic Monte Carlo ◽  
Continuous Phase ◽  
Determining Factors ◽  
Equilibrium And Kinetics ◽  
Kinetic Monte Carlo Simulations ◽  
The Stability ◽  
Stable Reconstruction

AbstractGrowth kinetics and thermodynamic equilibrium can both be determining factors at different stages of III-V semiconductor heteroepitaxy. We study their interplay, employing kinetic Monte Carlo simulations for the InAs(001) surface. The simulation contains atomistic details of both species, including the stability of different reconstructions and their kinetics. The behavior of the surface in thermodynamic equilibrium, including different reconstructions, is determined exclusively by extensive total energy calculations employing ab initio density functional theory. The continuous phase transition between the α?(2×4) and β?(2×4), predicted by theory, is confirmed by experiment. At full layer coverage, a recovery of the stable reconstruction is observed. The different time scales associated with As2 and In are discussed with respect to equilibrium and kinetics.

Effective Interactions Approach to Phase Stability in Alloys Under Irradiation

1998 ◽  
Vol 538 ◽  
Author(s):  
Raúl A. Enrique ◽  
Pascal Bellon
Keyword(s):  
Phase Diagram ◽  
Phase Stability ◽  
Kinetic Monte Carlo ◽  
Theoretical Frameworks ◽  
Effective Interactions ◽  
Dynamical Phase ◽  
Thermodynamic Potentials ◽  
Simple Kinetic Model ◽  
Kinetic Monte Carlo Simulations ◽  
Competing Dynamics

AbstractPhase stability in alloys under irradiation is studied considering effective thermodynamic potentials. A simple kinetic model of a binary alloy with phase separation is investigated. Time evolution in the alloy results from two competing dynamics: thermal diffusion, and irradiation induced ballistic exchanges. The dynamical (steady state) phase diagram is evaluated exactly performing Kinetic Monte Carlo simulations. The solution is then compared to two theoretical frameworks: the effective quasi-interactions model as proposed by Vaks and Kamishenko, and the effective free energy model as proposed by Martin. New developments of these models are proposed to allow for quantitative comparisons. Both theoretical frameworks yield fairly good approximations to the dynamical phase diagram.

scholarly journals Investigation of Hydrothermally Stressed Silicone Rubber/Silica Micro and Nanocomposite for the Coating High Voltage Insulation Applications

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3567
Author(s):  
Faiza Faiza ◽  
Abraiz Khattak ◽  
Safi Ullah Butt ◽  
Kashif Imran ◽  
Abasin Ulasyar ◽  
...  
Keyword(s):  
Silicone Rubber ◽  
Structural Changes ◽  
Polymer Chains ◽  
Hydrothermal Conditions ◽  
Silica Filler ◽  
Before And After ◽  
Aging Conditions ◽  
The Stability ◽  
Micro Silica ◽  
Applied Stresses

Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.

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