K0101 Defects Dynamics Simulations of Crystalline and Amorphous Materials

2010 ◽  
Vol 2010.9 (0) ◽  
pp. 51-52
Author(s):  
Yoji SHIBUTANI
Keyword(s):  
Amorphous Materials ◽  
Dynamics Simulations

scholarly journals Fate of MgSiO3 melts at core–mantle boundary conditions

2015 ◽  
Vol 112 (46) ◽  
pp. 14186-14190 ◽  
Author(s):  
Sylvain Petitgirard ◽  
Wim J. Malfait ◽  
Ryosuke Sinmyo ◽  
Ilya Kupenko ◽  
Louis Hennet ◽  
...  
Keyword(s):  
Amorphous Materials ◽  
High Pressures ◽  
Ab Initio Molecular Dynamics ◽  
Density Contrast ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Liquid Silicate ◽  
Diamond Anvil ◽  
Pressure Regime ◽  
Dynamics Simulations

One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth’s mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch–Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core–mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm3, which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm3, i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.

scholarly journals Shear Band Formation in Amorphous Materials under Oscillatory Shear Deformation

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 300 ◽  
Author(s):  
Nikolai V. Priezjev
Keyword(s):  
Shear Band ◽  
Shear Deformation ◽  
Amorphous Materials ◽  
Oscillatory Shear ◽  
Band Formation ◽  
Disordered Solids ◽  
Novel Processing ◽  
Number Of Cycles ◽  
Dynamics Simulations ◽  
Small Clusters

The effect of periodic shear on strain localization in disordered solids is investigated using molecular dynamics simulations. We consider a binary mixture of one million atoms annealed to a low temperature with different cooling rates and then subjected to oscillatory shear deformation with a strain amplitude slightly above the critical value. It is found that the yielding transition occurs during one cycle but the accumulation of irreversible displacements and initiation of the shear band proceed over larger number of cycles for more slowly annealed glasses. The spatial distribution and correlation function of nonaffine displacements reveal that their collective dynamics changes from homogeneously distributed small clusters to a system-spanning shear band. The analysis of spatially averaged profiles of nonaffine displacements indicates that the location of a shear band in periodically loaded glasses can be identified at least several cycles before yielding. These insights are important for the development of novel processing methods and prediction of the fatigue lifetime of metallic glasses.

Vibrational signatures of chemical- and density-induced structural changes in simulated amorphous silica

2014 ◽  
Vol 92 (7/8) ◽  
pp. 615-618
Author(s):  
Victoria R. Grandy ◽  
Kristin M. Poduska ◽  
Ivan Saika-Voivod
Keyword(s):  
Short Range ◽  
Amorphous Materials ◽  
Structural Changes ◽  
Local Order ◽  
Vibrational Modes ◽  
Nearest Neighbours ◽  
Simulation And Experiment ◽  
Dynamics Simulations ◽  
Induced Changes ◽  
Vibrational Density

Molecular dynamics simulations show that vibrational modes in glassy SiO2 are affected differently by density-induced changes to the structural order compared with those induced by specific cationic substitutions (Al, P, Na). Using standard measures of local and midrange positional order, we find that P disrupts network order in terms of second nearest neighbours, but preserves local order. In contrast, Al decreases local order while maintaining network order. Increased density preserves structural correlations in the network although the length scale shrinks. The complex short-range and long-range structural trends in these modified glasses coincide with changes in distinct regions in the vibrational density of states (VDOS). This suggests that a greater role for VDOS as a tool to link simulation and experiment in amorphous materials.

scholarly journals Computing inelastic neutron scattering spectra from molecular dynamics trajectories

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Thomas F. Harrelson ◽  
Makena Dettmann ◽  
Christoph Scherer ◽  
Denis Andrienko ◽  
Adam J. Moulé ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Neutron Scattering ◽  
Amorphous Materials ◽  
Inelastic Neutron Scattering ◽  
Computational Cost ◽  
Simulation Method ◽  
Inelastic Neutron ◽  
Phonon Modes ◽  
Structural Variety ◽  
Dynamics Simulations

AbstractInelastic neutron scattering (INS) provides a weighted density of phonon modes. Currently, INS spectra can only be interpreted for perfectly crystalline materials because of high computational cost for electronic simulations. INS has the potential to provide detailed morphological information if sufficiently large volumes and appropriate structural variety are simulated. Here, we propose a method that allows direct comparison between INS data with molecular dynamics simulations, a simulation method that is frequently used to simulate semicrystalline/amorphous materials. We illustrate the technique by analyzing spectra of a well-studied conjugated polymer, poly(3-hexylthiophene-2,5-diyl) (P3HT) and conclude that our technique provides improved volume and structural variety, but that the classical force field requires improvement before the morphology can be accurately interpreted.

scholarly journals Structure and Glass Transition Temperature of Amorphous Dispersions of Model Pharmaceuticals with Nucleobases from Molecular Dynamics

Pharmaceutics ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1253
Author(s):  
Ctirad Červinka ◽  
Michal Fulem
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Amorphous Materials ◽  
Computational Study ◽  
Pharmaceutical Ingredients ◽  
Quantitative Accuracy ◽  
Racemic Ibuprofen ◽  
Dynamics Simulations

Glass transition temperature (Tg) is an important material property, which predetermines the kinetic stability of amorphous solids. In the context of active pharmaceutical ingredients (API), there is motivation to maximize their Tg by forming amorphous mixtures with other chemicals, labeled excipients. Molecular dynamics simulations are a natural computational tool to investigate the relationships between structure, dynamics, and cohesion of amorphous materials with an all-atom resolution. This work presents a computational study, addressing primarily the predictions of the glass transition temperatures of four selected API (carbamazepine, racemic ibuprofen, indomethacin, and naproxen) with two nucleobases (adenine and cytosine). Since the classical non-polarizable simulations fail to reach the quantitative accuracy of the predicted Tg, analyses of internal dynamics, hydrogen bonding, and cohesive forces in bulk phases of pure API and their mixtures with the nucleobases are performed to interpret the predicted trends. This manuscript reveals the method for a systematic search of beneficial pairs of API and excipients (with maximum Tg when mixed). Monitoring of transport and cohesive properties of API–excipients systems via molecular simulation will enable the design of such API formulations more efficiently in the future.

scholarly journals Random critical point separates brittle and ductile yielding transitions in amorphous materials

2018 ◽  
Vol 115 (26) ◽  
pp. 6656-6661 ◽  
Author(s):  
Misaki Ozawa ◽  
Ludovic Berthier ◽  
Giulio Biroli ◽  
Alberto Rosso ◽  
Gilles Tarjus
Keyword(s):  
Critical Point ◽  
Amorphous Materials ◽  
Mean Field ◽  
Universality Class ◽  
Particle Interactions ◽  
Molecular Glasses ◽  
First Order ◽  
Initial Stability ◽  
Dynamics Simulations

We combine an analytically solvable mean-field elasto-plastic model with molecular dynamics simulations of a generic glass former to demonstrate that, depending on their preparation protocol, amorphous materials can yield in two qualitatively distinct ways. We show that well-annealed systems yield in a discontinuous brittle way, as metallic and molecular glasses do. Yielding corresponds in this case to a first-order nonequilibrium phase transition. As the degree of annealing decreases, the first-order character becomes weaker and the transition terminates in a second-order critical point in the universality class of an Ising model in a random field. For even more poorly annealed systems, yielding becomes a smooth crossover, representative of the ductile rheological behavior generically observed in foams, emulsions, and colloidal glasses. Our results show that the variety of yielding behaviors found in amorphous materials does not necessarily result from the diversity of particle interactions or microscopic dynamics but is instead unified by carefully considering the role of the initial stability of the system.

AEM analysis of crystallization in Ti-based amorphous alloys

1983 ◽  
Vol 41 ◽  
pp. 270-271
Author(s):  
A.R. Pelton ◽  
A.F. Marshall ◽  
Y.S. Lee
Keyword(s):  
Magnetic Properties ◽  
Amorphous Alloys ◽  
Amorphous Materials ◽  
Isothermal Annealing ◽  
Amorphous Matrix ◽  
Nucleation And Growth ◽  
Current Interest ◽  
Amorphous Films ◽  
Electrical And Magnetic Properties

Amorphous materials are of current interest due to their desirable mechanical, electrical and magnetic properties. Furthermore, crystallizing amorphous alloys provides an avenue for discerning sequential and competitive phases thus allowing access to otherwise inaccessible crystalline structures. Previous studies have shown the benefits of using AEM to determine crystal structures and compositions of partially crystallized alloys. The present paper will discuss the AEM characterization of crystallized Cu-Ti and Ni-Ti amorphous films.Cu60Ti40: The amorphous alloy Cu60Ti40, when continuously heated, forms a simple intermediate, macrocrystalline phase which then transforms to the ordered, equilibrium Cu3Ti2 phase. However, contrary to what one would expect from kinetic considerations, isothermal annealing below the isochronal crystallization temperature results in direct nucleation and growth of Cu3Ti2 from the amorphous matrix.

TEM studies of amorphization processes and amorphous structures

1988 ◽  
Vol 46 ◽  
pp. 448-449
Author(s):  
T. E. Mitchell ◽  
R. B. Schwarz
Keyword(s):  
Amorphous Materials ◽  
Fission Products ◽  
Rapid Quenching ◽  
Surface Films ◽  
List Type ◽  
Oxide Glasses ◽  
Crystalline Materials ◽  
Amorphous Structures ◽  
Amorphous Surface ◽  
Interfacial Films

Traditional oxide glasses occur naturally as obsidian and can be made easily by suitable cooling histories. In the past 30 years, a variety of techniques have been discovered which amorphize normally crystalline materials such as metals. These include [1-3]:Rapid quenching from the vapor phase.Rapid quenching from the liquid phase.Electrodeposition of certain alloys, e.g. Fe-P.Oxidation of crystals to produce amorphous surface oxide layers.Interdiffusion of two pure crystalline metals.Hydrogen-induced vitrification of an intermetal1ic.Mechanical alloying and ball-milling of intermetal lie compounds.Irradiation processes of all kinds using ions, electrons, neutrons, and fission products.We offer here some general comments on the use of TEM to study these materials and give some particular examples of such studies.Thin specimens can be prepared from bulk homogeneous materials in the usual way. Most often, however, amorphous materials are in the form of surface films or interfacial films with different chemistry from the substrates.

Analysis of Dark-Field Images of Disordered Materials

1972 ◽  
Vol 30 ◽  
pp. 560-561
Author(s):  
J. M. Cowley
Keyword(s):  
Amorphous Materials ◽  
Careful Analysis ◽  
Dark Field ◽  
Minimum Diameter ◽  
Statistical Fluctuations ◽  
Bright Spots ◽  
Sufficient Detail ◽  
Random Arrangement ◽  
Diffraction Patterns ◽  
Imaging Conditions

Recently a number of authors have reported detail in dark-field images obtained from diffuse-scattering regions of electron diffraction patterns. Bright spots in images from short-range order diffuse peaks of disordered binary alloys have been interpreted as evidence for the existence of microdomains of ordered lattice or of segragated clusters of one component. Spotty contrast in dark field images of near-amorphous materials has been interpreted as evidence for the existense of microcrystals. Without a careful analysis of the imaging conditions such conclusions may be invalid. Usually the conditions of the experiment have not been specified in sufficient detail to allow evaluation of the conclusions.Elementary considerations show that even for a completely random arrangement of atoms the statistical fluctuations of density will give a spotty contrast with spots of minimum diameter determined by the dark field aperture size and other factors influencing the minimum resolvable distance under darkfield imaging conditions, including fluctuations and drift over long exposure times (resolution usually 10Å or more).

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