scholarly journals Distinct signature of local tetrahedral ordering in the scattering function of covalent liquids and glasses

2019 ◽  
Vol 5 (3) ◽  
pp. eaav3194 ◽  
Author(s):  
Rui Shi ◽  
Hajime Tanaka
Keyword(s):  
Amorphous Materials ◽  
Covalent Bonding ◽  
Diffraction Peak ◽  
Wave Number ◽  
Direct Measure ◽  
Scattering Function ◽  
Tetrahedral Unit ◽  
Amorphous Structures ◽  
Extract Information

Tetrahedral amorphous materials such as SiO2, GeO2, Si, Ge, C, and chalcogenides are extremely important in nature and technology. It is known that covalent bonding favors local tetrahedral order in these materials. However, how to extract information on this structural order from the scattering function has remained elusive. By analyzing the structure of simulated SiO2 and experimental data of various tetrahedral materials, we show that the lowest wave number peak, known as the first sharp diffraction peak (FSDP), and a few higher wave number ones in the scattering functions come from the characteristic density waves of a single tetrahedral unit. FSDP is thus a direct measure of the tetrahedrality. This finding opens the door for long-awaited experimental access to the characterization of disordered amorphous structures.

Characterization of Amorphous Materials by Electron Diffraction and Atomistic Modeling

2000 ◽  
Vol 6 (4) ◽  
pp. 329-334 ◽  
Author(s):  
D.J.H. Cockayne ◽  
D.R. McKenzie ◽  
W. McBride ◽  
C. Goringe ◽  
D. McCulloch
Keyword(s):  
Molecular Dynamics ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Amorphous Materials ◽  
Atomistic Modeling ◽  
Amorphous Structures

AbstractThe technique of energy selected electron diffraction gives information about amorphous structures which can be used to characterize amorphous materials in terms of their structure. The diffraction data can be used to refine models obtained using molecular dynamics, resulting in physically reasonable models consistent with the diffraction data.

Characterization of Amorphous Materials by Electron Diffraction and Atomistic Modeling

2000 ◽  
Vol 6 (4) ◽  
pp. 329-334
Author(s):  
D.J.H. Cockayne ◽  
D.R. McKenzie ◽  
W. McBride ◽  
C. Goringe ◽  
D. McCulloch
Keyword(s):  
Molecular Dynamics ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Amorphous Materials ◽  
Atomistic Modeling ◽  
Amorphous Structures

Abstract The technique of energy selected electron diffraction gives information about amorphous structures which can be used to characterize amorphous materials in terms of their structure. The diffraction data can be used to refine models obtained using molecular dynamics, resulting in physically reasonable models consistent with the diffraction data.

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.

Coherent electron nanodiffraction from clean silver nano particles in a UHV STEM

1993 ◽  
Vol 51 ◽  
pp. 1058-1059
Author(s):  
J. Liu ◽  
M. Pan ◽  
G. E. Spinnler
Keyword(s):  
Supported Catalysts ◽  
Imaging Techniques ◽  
Nano Particles ◽  
Metal Particles ◽  
Shape Structure ◽  
Dynamical Simulations ◽  
Small Metal Particles ◽  
Extract Information

Small metal particles have peculiar chemical and physical properties as compared to bulk materials. They are especially important in catalysis since metal particles are common constituents of supported catalysts. The structural characterization of small particles is of primary importance for the understanding of structure-catalytic activity relationships. The shape and size of metal particles larger than approximately 5 nm in diameter can be determined by several imaging techniques. It is difficult, however, to deduce the shape of smaller metal particles. Coherent electron nanodiffraction (CEND) patterns from nano particles contain information about the particle size, shape, structure and defects etc. As part of an on-going program of STEM characterization of supported catalysts we report some preliminary results of CEND study of Ag nano particles, deposited in situ in a UHV STEM instrument, and compare the experimental results with full dynamical simulations in order to extract information about the shape of Ag nano particles.

Characterization of Flood Waves by Rating Curves

1997 ◽  
Vol 28 (1) ◽  
pp. 51-64 ◽  
Author(s):  
S.K. Mishra ◽  
M.K. Jain ◽  
S.M. Seth
Keyword(s):  
Phase Difference ◽  
Central India ◽  
Wave Number ◽  
Wave Characteristics ◽  
Travel Wave ◽  
Frame Work ◽  
Rating Curves ◽  
Exact Relationship ◽  
Flood Waves

The flood waves are characterized within the frame-work of loop (or hysteresis) of rating curves. The National Weather Service's Dam Break Flood Forecasting Model is used to generate the flood waves in the downstream valley of the Bargi dam located in Central India. The quantified hystereses, η, of non-dimensional rating curves are related with the corresponding flood wave characteristics, viz., speed of travel, wave number, phase difference, and attenuation. The analysis has led to the development of an exact relationship between η and phase difference. Using the concept of wave zoning, the better performance of the hysteresis based criteria compared with the available criteria is verified using Convex and Muskingum-Cunge routing in the wave zones. η limits are specified for the applicability of these simplified routing models. Furthermore, the envisaged applications of the based analysis are introduced.

scholarly journals Crystalline shielding mitigates structural rearrangement and localizes memory in jammed systems under oscillatory shear

2021 ◽  
Vol 7 (20) ◽  
pp. eabe3392
Author(s):  
Erin G. Teich ◽  
K. Lawrence Galloway ◽  
Paulo E. Arratia ◽  
Danielle S. Bassett
Keyword(s):  
Local Structure ◽  
Disordered Systems ◽  
Amorphous Materials ◽  
Structural Rearrangement ◽  
Oscillatory Shear ◽  
Disordered Materials ◽  
Rheological Measurements ◽  
Particle Level ◽  
Individual Particles

The nature of yield in amorphous materials under stress has yet to be fully elucidated. In particular, understanding how microscopic rearrangement gives rise to macroscopic structural and rheological signatures in disordered systems is vital for the prediction and characterization of yield and the study of how memory is stored in disordered materials. Here, we investigate the evolution of local structural homogeneity on an individual particle level in amorphous jammed two-dimensional (athermal) systems under oscillatory shear and relate this evolution to rearrangement, memory, and macroscale rheological measurements. We define the structural metric crystalline shielding, and show that it is predictive of rearrangement propensity and structural volatility of individual particles under shear. We use this metric to identify localized regions of the system in which the material’s memory of its preparation is preserved. Our results contribute to a growing understanding of how local structure relates to dynamic response and memory in disordered systems.

scholarly journals Synthesis and Characterization of Sugarcane Bagasse Based Activated Carbon: Effect of Impregnation Ratio of ZnCl2

2020 ◽  
Vol 41 (1) ◽  
pp. 74-79
Author(s):  
Sahira Joshi ◽  
Bishnu K.C.
Keyword(s):  
Iodine Number ◽  
Surface Area ◽  
Sugarcane Bagasse ◽  
Amorphous Materials ◽  
Activated Carbons ◽  
X Ray Diffraction ◽  
Impregnation Ratio ◽  
Methylene Blue Number ◽  
Xrd Patterns

Series of activated carbons (ACs) have been prepared from Sugarcane bagasse powder by ZnCl2 activation at various impregnation ratios of ZnCl2 to Sugarcane bagasse powder of 0.25:1, 0.5:1, 1:1 and 2:1 by weight. Characteristics of the activated carbons (ACs) were determined by iodine number, methylene blue number, surface area, scanning electron microscopy (SEM) and x-ray diffraction. Iodine number (IN) indicated that, microporosity of the AC were increased with increasing impregnation ratio ZnCl2 to Sugarcane bagasse upto 1:1 then started to decrease. However, mesoporosity as well as surface area was increased progressively. The maximum value of iodine number (868 mg/g) was achieved in the AC prepared at impregnation ratio of ZnCl2 to sugarcane bagasse 1:1. SEM micrographs also show the presence of well developed pores on its surface of AC-1. The broad peaks in the XRD patterns indicated that, all the ACs is amorphous materials. From results, it is concluded that ZnCl2 concentration used in impregnation is effective for development of porosity and surface area of the AC prepared from Sugarcane bagasse.

The Influence of Argon Pressure on the Structural and Physical Properties of LaB6 Films

2011 ◽  
Vol 55-57 ◽  
pp. 1436-1440 ◽  
Author(s):  
Xiao Hua Zhao ◽  
Guang Hui Min ◽  
Jing Xu ◽  
Jie Lin
Keyword(s):  
Physical Properties ◽  
Elasticity Modulus ◽  
Lanthanum Hexaboride ◽  
Argon Pressure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Force Microscopy ◽  
Amorphous Structures ◽  
Crystallization Degree

Lanthanum hexaboride (LaB6) films were deposited on Si (111) substrates by magnetron sputtering method. The characterization of the films was investigated by means of atom force microscopy (AFM), X-ray diffraction (XRD), four-point probe electrical resistance measurement, scratch tester and nano-indentation tester. Influence of argon pressure on physical properties, such as crystallization degree, conductivity and mechanical properties was studied. All the films were smooth and dense. The film crystallites showed a preferential orientation of (100) plane, but the films which were deposited at 2.0 Pa exhibited amorphous structures. LaB6 films which were deposited below 1.5 Pa had excellent conductivity. The bonding strength of the films which were deposited at 1.0 Pa was higher than the others due to the formation of the nano-sized crystals. The hardness and elastic modulus were investigated in connection with the crystalline of LaB6 films. As a result, the films which were deposited at 1.0 Pa had a maximal value of hardness (16.782 Gpa) and elasticity modulus (193.895 Gpa). In a word, the LaB6 films which were deposited at 1.0 Pa have a higher degree of crystalline and more excellent physical properties in comparison with the others. The obtained results will be used synthesizing LaB6 films for applications in low-temperature thermoelectric devices.

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