scholarly journals Effect of cooling rate on structural transformations in Ti-Al-V nanoalloy: molecular dynamics study

2021 ◽  
Vol 2052 (1) ◽  
pp. 012038
Author(s):  
N Yu Sdobnyakov ◽  
V M Samsonov ◽  
V S Myasnichenko ◽  
P M Ershov ◽  
A N Bazulev ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Size Effect ◽  
Cooling Rate ◽  
Tight Binding ◽  
Structural Transformations ◽  
Rate Effect ◽  
Binding Potential ◽  
Cooling Rates ◽  
Thermally Induced ◽  
Local Structures

Abstract Using the isothermal molecular dynamics and the tight-binding potential, crystallization of Ti6Al4V nanodroplets was simulated. The objects of the research consisted of 2869 atoms, including 172 Al atoms and 115 V ones. The OVITO program was employed to recognize local structures and nanophases arisen in the course of cooling nanoalloy with the cooling rates of 0.1 and 0.4 K/ps. We have found that the cooling rate effect on the structure of the Ti6Al4V nanoalloy and the thermally induced structural transformations is much more pronounced than the size effect.

scholarly journals SIMULATION OF THE FRACTAL METAL FILMS FORMATION

2020 ◽  
pp. 424-437
Author(s):  
Дмитрий Викторович Иванов ◽  
Сергей Александрович Васильев ◽  
Николай Юрьевич Сдобняков ◽  
Елена Владимировна Романовская ◽  
Виталий Александрович Анофриев ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Beam ◽  
Gold Film ◽  
Tight Binding ◽  
Copper Surface ◽  
Metal Films ◽  
Binding Potential ◽  
Fractal Structures ◽  
Software Product ◽  
Dynamics Method

В данной работе методом молекулярной динамики с использованием потенциала сильной связи проведено моделирование процесса молекулярно-лучевой эпитаксии с целью определения закономерностей при формировании фрактальных металлических пленок на твердой поверхности. В качестве подложки использовалась медь, пленка формировалась из атомов золота. Показана возможность формирования фрактальных структур в островковой пленке золота на поверхности меди. Различными аналитическими методами с использованием программного продукта Gwyddion проанализирован диапазон изменения фрактальной размерности при различных условиях молекулярно-динамического эксперимента. In this work, molecular dynamics method and the tight binding potential was used to simulate the process of the molecular beam epitaxy in order to determine regularities in the formation of fractal metal films on a solid surface. Copper was used as a substrate, the film was formed from gold atoms. The possibility of formation of fractal structures in an island gold film on the copper surface is shown. Various analytical methods using the Gwyddion software product have used to analyze a range of changes in the fractal dimension under different conditions of molecular dynamics experiment.

scholarly journals STRUCTURAL STABILITY OF Ag AND Ag NANOCLUSTERS WITH A CHANGE IN THE INITIAL MORPHOLOGY

2021 ◽  
pp. 604-611
Author(s):  
Дарья Антоновна Рыжкова ◽  
Светлана Леонидовна Гафнер ◽  
Юрий Яковлевич Гафнер
Keyword(s):  
Tight Binding ◽  
Thermal Relaxation ◽  
Silver Nanoclusters ◽  
Binding Potential ◽  
Magic Numbers ◽  
Structural Transitions ◽  
Thermally Induced ◽  
Second Moment ◽  
Moment Approximation ◽  
Dynamics Method

В статье методом молекулярной динамики с использованием модифицированного потенциала сильной связи TB-SMA (second moment approximation of tight-binding) проводится сравнительный анализ характера термически индуцированных структурных переходов в нанокластерах серебра, число атомов в которых соответствует «магическим» числам икосаэдрической структуры, при вариации их начальной морфологии. Показано, что в случае начальной ГЦК конфигурации формирование Ih модификации происходит либо на этапе предварительной термической релаксации, либо в ходе дальнейшего нагрева. При начальной аморфной морфологии характер структурных переходов претерпевает значительные изменения. Так, например, формирующаяся Ih модификация обладает большей стабильностью в области высоких температур и точка плавления нанокластеров смещается на величину более 100 К. Такой эффект обусловлен более плавным изменением удельной потенциальной энергии нанокластера в сравнении со случаем, когда устойчивая Ih конфигурация формируется при низких температурах. Полученные данные могут быть использованы при процессах создания нанокластеров серебра с требуемым внутренним строением. This article provides a comparative analysis of thermally induced structural transitions in silver nanoclusters with a change in their initial morphology. The study was executed by the molecular dynamics method using the modified TB-SMA (second moment approximation of tight-binding) tight binding potential. The number of atoms in nanoclusters corresponds to the icosahedral structure «magic» numbers. It is shown that for nanoclusters with the initial FCC configuration, the Ih modification is formed either at the stage of preliminary thermal relaxation or during further heating. For nanoclusters with an initial amorphous morphology, the nature of structural transitions undergoes significant changes. For example, the formed Ih modification is more stable at high temperatures and the melting point of nanoclusters shifts by more than 100 K. This effect is due to a smoother change in the specific potential energy of the nanocluster in comparison with the case when a stable Ih configuration is formed at low temperatures. The data obtained can be used in processes to create silver nanoclusters with the required internal structure.

scholarly journals Оценка влияния икосаэдрических "магических" чисел на термическую стабильность малых нанокластеров серебра

2022 ◽  
Vol 64 (3) ◽  
pp. 313
Author(s):  
Д.А. Рыжкова ◽  
С.Л. Гафнер ◽  
Ю.Я. Гафнер
Keyword(s):  
Tight Binding ◽  
Thermal Relaxation ◽  
Silver Nanoclusters ◽  
Binding Potential ◽  
Magic Numbers ◽  
Structural Transitions ◽  
Icosahedral Structure ◽  
Thermally Induced ◽  
Fcc Phase ◽  
Dynamics Method

A comparative analysis of thermally induced structural transitions in silver nanoclusters, the number of atoms of which corresponded to the “magic” numbers of the icosahedral (Ih) structure with variation of their initial morphology, was carried out by the molecular dynamics method using the modified tight-binding potential TB-SMA. It is shown that, in the case of the initial fcc phase, the formation of the Ih modification, depending on the particle size, occurred either at the stage of preliminary thermal relaxation or during further heating. At the initial amorphous morphology, the nature of the structural transitions underwent significant changes. Thus, even in the case of Ag55 clusters, the icosahedral structure was formed only in 50-60% of the experiments performed. Based on the data obtained, it was concluded that to create a stable Ih structure, it is necessary to use the thermal cycling procedure.

Large-Scale Molecular Dynamics Simulations of Interstitial Defect Diffusion in Silicon

2002 ◽  
Vol 731 ◽  
Author(s):  
David A. Richie ◽  
Jeongnim Kim ◽  
Richard Hennig ◽  
Kaden Hazzard ◽  
Steve Barr ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Large Scale ◽  
Materials Science ◽  
Tight Binding ◽  
Md Simulations ◽  
Binding Potential ◽  
Interstitial Defect ◽  
Long Time ◽  
Computational Materials ◽  
Dynamics Simulations

AbstractThe simulation of defect dynamics and evolution is a technologicaly relevant challenge for computational materials science. The diffusion of small defects in silicon unfolds as a sequence of structural transitions. The relative infrequency of transition events requires simulation over extremely long time scales. We simulate the diffusion of small interstitial clusters (I1, I2, I3) for a range of temperatures using large-scale molecular dynamics (MD) simulations with a realistic tight-binding potential. A total of 0.25 μ sec of simulation time is accumulated for the study. A novel real-time multiresolution analysis (RTMRA) technique extracts stable structures directly from the dynamics without structural relaxation. The discovered structures are relaxed to confirm their stability.

scholarly journals SIMULATION OF LAYER BY LAYER GROWTH OF FRACTAL METAL Pt-Rh FILMS

2021 ◽  
pp. 682-692
Author(s):  
Дмитрий Викторович Иванов ◽  
Виталий Александрович Анофриев ◽  
Владимир Александрович Кошелев ◽  
Александр Сергеевич Антонов ◽  
Сергей Александрович Васильев ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Image Analysis ◽  
Fractal Dimension ◽  
Tight Binding ◽  
Computer Experiment ◽  
Layer Growth ◽  
Binding Potential ◽  
Layer By Layer ◽  
Fractal Structures ◽  
Continuous Film

В данной работе методом молекулярной динамики с использованием потенциала сильной связи проведено моделирование процесса молекулярно-лучевой эпитаксии с целью определения закономерностей при формировании фрактальных металлических пленок платины на поверхности родия. Установлена возможность формирования фрактальных структур как в островковых пленках платины на поверхности родия, так и в сплошной пленке. Установлены параметры компьютерного эксперимента, определяющие переход от отдельных островковых пленок к сплошной пленке в указанной системе. С использованием различных программных продуктов Gwyddion и Image Analysis, а также собственной разработки FractalSurface проанализирован диапазон изменения фрактальной размерности при различных условиях молекулярно-динамического эксперимента методом подсчета кубов. Полученные значения фрактальной размерности в целом находятся в приемлемом согласии между собой, однако существует ряд исключений, которые обсуждаются более подробно. Сравнительный анализ получаемых результатов позволяет формулировать рекомендации для методики создания, корректировки и прецизионного контроля при «выращивании» структур с заданной морфологией поверхности. In this work, the molecular dynamics method and the tight-binding potential are used to simulate the process of molecular beam epitaxy in order to determine the regularities in the formation of fractal platinum metal films on the rhodium surface. The possibility of formation of fractal structures both in island platinum films on the rhodium surface and in a continuous film has been established. The parameters of the computer experiment, which determine the transition from individual island films to a continuous film in the indicated system, have been established. Using various software products Gwyddion and Image Analysis, as well as our own software FractalSurface, the range of changes in the fractal dimension has been analyzed under various conditions of a molecular dynamics experiment by the method of cube counting. The obtained values of the fractal dimension are generally in acceptable agreement with each other; however, there is a number of exceptions, which are discussed in more detail. A comparative analysis of the results obtained allows one to formulate recommendations for the methodology for creating, adjusting and precision control when «growing» structures with a given surface morphology.

Experimental test of the cooling rate effect on blocking temperatures in stepwise thermal demagnetization

2020 ◽  
Vol 224 (2) ◽  
pp. 1116-1126
Author(s):  
Thomas A Berndt ◽  
Liao Chang ◽  
Greig A Paterson ◽  
Changqian Cao
Keyword(s):  
Relaxation Time ◽  
Cooling Rate ◽  
Experimental Test ◽  
High Accuracy ◽  
Rate Effect ◽  
Blocking Temperature ◽  
Controlled Cooling ◽  
Cooling Rates ◽  
Thermal Demagnetization ◽  
Theoretical Predictions

SUMMARY Upon cooling, most rocks acquire a thermoremanent magnetization (TRM); the cooling rate at which this happens not only affects palaeointensity estimates, but also their unblocking temperatures in stepwise thermal demagnetization experiments, which is important, for example, to estimate volcanic emplacement temperatures. Traditional single-domain (SD) theory of magnetic remanence relates relaxation times to blocking temperatures— the blocking temperature is the temperature at which the relaxation time becomes shorter than the experimental timescale—and therefore strictly only applies to remanence acquisition mechanisms at constant temperatures (i.e. viscous remanent magnetizations, VRMs). A theoretical framework to relate (constant) blocking temperatures to (time-varying) cooling rates exists, but this theory has very limited experimental verification—partly due to the difficulty of accurately knowing the cooling rates of geological materials. Here we present an experimental test of this ‘cooling rate effect on blocking temperatures’ through a series of demagnetization experiments of laboratory-induced TRMs with controlled cooling rates. The tested cooling rates span about 1 order of magnitude and are made possible through (1) extremely accurate demagnetization experiments using a low-temperature magnetic properties measurement system (MPMS) and (2) the use of a ‘1-step-only’ stepwise thermal demagnetization protocol where the relaxation process is measured over time. In this way the relaxation time corresponding to the blocking temperature is measured, which can be done to much higher accuracy than measuring the blocking temperature directly as done in traditional stepwise thermal demagnetization experiments. Our experiments confirm that the cooling rate relationship holds to high accuracy for ideal magnetic recorders, as shown for a synthetic weakly interacting SD magnetoferritin sample. A SD-dominated low-Ti titanomagnetite Tiva Canyon Tuff sample, however, showed that natural samples are unlikely to be sufficiently ‘ideal’ to meet the theoretical predictions to high accuracy—the experimental data agrees only approximately with the theoretical predictions, which may potentially affect blocking temperature estimates in stepwise thermal demagnetization experiments. Moreover, we find a strongly enhanced cooling rate effect on palaeointensities for even marginally non-ideal samples (up to 43 per cent increase in pTRM for a halving of the cooling rate).

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