Probing the Structure of Melts, Glasses, and Amorphous Materials

Elements ◽  
2021 ◽  
Vol 17 (3) ◽  
pp. 175-180 ◽  
Author(s):  
Chris J. Benmore ◽  
Martin C. Wilding
Keyword(s):  
Neutron Diffraction ◽  
Amorphous Materials ◽  
Hydrothermal Activity ◽  
Crystalline Materials ◽  
Geological Processes ◽  
Atomistic Models ◽  
Glassy Materials ◽  
Amorphous States ◽  
And Behavior ◽  
Frictional Melting

Liquids, glasses, and amorphous materials are ubiquitous in the Earth sciences and are intrinsic to a plethora of geological processes, ranging from volcanic activity, deep Earth melting events, metasomatic processes, frictional melting (pseudotachylites), lighting strikes (fulgurites), impact melting (tektites), hydrothermal activity, aqueous solution geochemistry, and the formation of dense high-pressure structures. However, liquids and glassy materials lack the long-range order that characterizes crystalline materials, and studies of their structure require a different approach to that of conventional crystallography. The pair distribution function is the neutron diffraction technique used to characterize liquid and amorphous states. When combined with atomistic models, neutron diffraction techniques can determine the properties and behavior of disordered structures.

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.

scholarly journals Ultrafast calculation of diffuse scattering from atomistic models

2019 ◽  
Vol 75 (1) ◽  
pp. 14-24 ◽  
Author(s):  
Joseph A. M. Paddison
Keyword(s):  
Diffuse Scattering ◽  
Large Data ◽  
Large Data Sets ◽  
Scattering Data ◽  
Frequency Noise ◽  
Data Sets ◽  
Fast Method ◽  
Crystalline Materials ◽  
Atomistic Models ◽  
Dynamics Simulations

Diffuse scattering is a rich source of information about disorder in crystalline materials, which can be modelled using atomistic techniques such as Monte Carlo and molecular dynamics simulations. Modern X-ray and neutron scattering instruments can rapidly measure large volumes of diffuse-scattering data. Unfortunately, current algorithms for atomistic diffuse-scattering calculations are too slow to model large data sets completely, because the fast Fourier transform (FFT) algorithm has long been considered unsuitable for such calculations [Butler & Welberry (1992). J. Appl. Cryst. 25, 391–399]. Here, a new approach is presented for ultrafast calculation of atomistic diffuse-scattering patterns. It is shown that the FFT can actually be used to perform such calculations rapidly, and that a fast method based on sampling theory can be used to reduce high-frequency noise in the calculations. These algorithms are benchmarked using realistic examples of compositional, magnetic and displacive disorder. They accelerate the calculations by a factor of at least 102, making refinement of atomistic models to large diffuse-scattering volumes practical.

scholarly journals Tunable continuous wave emission via phase-matched second harmonic generation in a ZnSe microcylindrical resonator

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
N. Vukovic ◽  
N. Healy ◽  
J. R. Sparks ◽  
J. V. Badding ◽  
P. Horak ◽  
...  
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Amorphous Materials ◽  
Continuous Wave ◽  
Frequency Comb ◽  
Second Harmonic ◽  
Red Light ◽  
Nonlinear Phenomena ◽  
Optical Processing ◽  
Crystalline Materials

Abstract Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena. Compared to amorphous materials, crystalline structures often exhibit desirable properties such as high indices of refraction, high nonlinearities and large windows of transparency, making them ideal for use in frequency comb generation, microlasing and all-optical processing. In particular, crystalline materials can also possess a non-centrosymmetric structure which gives rise to the second order nonlinearity, necessary for three photon processes such as frequency doubling and parametric down-conversion. Here we report a novel route to fabricating crystalline zinc selenide microcylindrical resonators from our semiconductor fibre platform and demonstrate their use for tunable, low power continuous wave second harmonic generation. Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator. By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500–22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

Multiple-data-set Rietveld analysis using isotopes in powder neutron diffraction. 2. Positional and anisotropic thermal displacement parameter determinations in CuO (tenorite) at 2 K and 300 K

2003 ◽  
Vol 36 (2) ◽  
pp. 206-212
Author(s):  
Paul F. Henry ◽  
Harriott Nowell ◽  
Mark T. Weller ◽  
Chick C. Wilson
Keyword(s):  
Neutron Diffraction ◽  
Structural Parameters ◽  
Rietveld Analysis ◽  
Data Set ◽  
Crystalline Materials ◽  
Multiple Data ◽  
Analysis Technique ◽  
Precision And Accuracy ◽  
Single Data ◽  
Combined Data

The technique of isotope-substitution neutron diffraction (ISND) and combined-data-set Rietveld analysis from powder neutron data of crystalline materials is presented and compared with single-data-set powder refinement methods. The rationale behind improvements in the precision and accuracy of the refined model as a result of reduction in parameter correlation in the least-squares technique is described. The improvements are demonstrated practically through a study of isotopically copper-substituted tenorite, CuO, at 2 and 300 K. Typically, the estimated errors on structural parameters from the combined analysis technique are 30% lower than separate single-data-set analyses. Comparison of the precision and accuracy of the structural models obtained from this investigation with previous single-crystal X-ray studies are also presented.

MULTISCALE MODELING FOR AMORPHOUS MATERIALS — MAPPING ATOMISTIC DISPLACEMENTS TO MACROSCOPIC DEFORMATION

2012 ◽  
Vol 04 (04) ◽  
pp. 1250037 ◽  
Author(s):  
ZHOU CHENG SU ◽  
TONG-EARN TAY ◽  
YU CHEN ◽  
VINCENT B. C. TAN
Keyword(s):  
Amorphous Materials ◽  
Amorphous Material ◽  
Multiscale Simulations ◽  
Mathematical Form ◽  
Computational Domain ◽  
Crystalline Materials ◽  
Macroscopic Deformation ◽  
T Matrix ◽  
Representative Points ◽  
Good Agreement

A method to relate the displacements of atoms within a representative volume element (RVE) of amorphous material to the deformation of the RVE is presented. The displacement relationship is expressed as a mapping matrix, T, which operates on the displacements of representative points in the RVE to return the atom displacements within it. While the mapping operation has the same mathematical form as an interpolation operation, the T matrix is not an interpolant. It is derived taking into account atom displacements in amorphous materials which cannot be simplified as a continuous, much less homogenous, field. It is shown that the computational domain of a material can be partitioned into nonintersecting sub-domains comprising representative cells — pseudo-amorphous cells (PAC) — and sub-domains of atoms for concurrent multiscale simulations of amorphous materials through the T matrix. Multiscale simulations of nanoindentation on a polymer substrate using the T matrix show good agreement with pure molecular mechanics simulations. When homogenization techniques commonly used for crystalline materials were employed for the same simulations, they gave much less accurate predictions.

scholarly journals PDF Analysis on a Laboratory System: Adapting the Experiment to the Material

2014 ◽  
Vol 70 (a1) ◽  
pp. C870-C870
Author(s):  
Céleste Reiss ◽  
Milen Gateshki ◽  
Marco Sommariva
Keyword(s):  
Distribution Function ◽  
Pair Distribution Function ◽  
Amorphous Materials ◽  
Nearest Neighbors ◽  
High Energy ◽  
Experimental Point ◽  
Laboratory System ◽  
Crystalline Materials ◽  
X Ray ◽  
Pdf Analysis

The increased interest in recent years regarding the properties and applications of nanomaterials has also created the need to characterize the structures of these materials. However, due to the lack of long-range atomic ordering, the structures of nanostructured and amorphous materials are not accessible by conventional diffraction methods used to study crystalline materials. One of the most promising techniques to study nanostructures using X-ray diffraction is by using the total scattering (Bragg peaks and diffuse scattering) from the samples and the pair distribution function (PDF) analysis. The pair distribution function provides the probability of finding atoms separated by a certain distance. This function is not direction-dependent; it only looks at the absolute value of the distance between the nearest neighbors, the next nearest neighbors and so on. The method can therefore also be used to analyze non-crystalline materials. From experimental point of view a typical PDF analysis requires the use of intense high-energy X-ray radiation (E ≥ 20 KeV) and a wide 2θ range. After the initial feasibility studies regarding the use of standard laboratory diffraction equipment for PDF analysis [1-3] this application has been further developed to achieve improved data quality and to extend the range of materials, environmental conditions and geometrical configurations that can be used for PDF experiments. Studies performed on different nanocrystalline and amorphous materials of scientific and technological interest, including organic substances, oxides, metallic alloys, etc. have demonstrated that PDF analysis with a laboratory diffractometer can be a valuable tool for structural characterization of nanomaterials. This contribution presents several examples of laboratory PDF studies, in which the experimental conditions have been successfully adapted to match the specific requirements of materials under investigation.

scholarly journals EVALUATION OF REFLECTANCE FOR BUILDING MATERIALS CLASSIFICATION WITH TERRESTRIAL LASER SCANNER RADIATION

2021 ◽  
Vol 61 (1) ◽  
pp. 174-198
Author(s):  
Domenica Costantino ◽  
Massimiliano Pepe ◽  
Maria Giuseppa Angelini
Keyword(s):  
Laser Scanning ◽  
Amorphous Materials ◽  
Building Materials ◽  
Phase Measurement ◽  
Laser Scanner ◽  
Optical Diffraction ◽  
Degree Of Crystallinity ◽  
Crystalline Materials ◽  
Oblique Position ◽  
Reflectance Analysis

The main purpose of this work is the evaluation of the potential of Terrestrial Laser Scanning (TLS) technology to perform a reflectance analysis of scanned objects. A laser beam, having a coherent beam in the field of visible light (wavelength between 532nm and 680 nm), can lead to optical diffraction phenomena that allow a correlation between the degree of crystallinity of solids (in particular dispersed crystalline materials) and its reflectivity. Different materials with known crystallinity values have been examined and the diffraction value has been analysed for two types of lasers, one pulsed and the other phase measurement, with two different acquisition conditions (nadiral and oblique position). The results demonstrated the correlation by verifying that the incident laser light beam is more refracted by materials with a higher degree of crystallinity than less crystalline or amorphous materials.

Determination of Crystal Thickness from Relative Transmission Measurements

1975 ◽  
Vol 33 ◽  
pp. 242-243 ◽  
Author(s):  
D. C. Joy ◽  
D. M. Maher
Keyword(s):  
Amorphous Materials ◽  
Accurate Estimate ◽  
Foil Thickness ◽  
Specimen Thickness ◽  
Crystal Thickness ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Relative Transmission ◽  
History Of ◽  
Electron Intensity

An accurate knowledge of the specimen foil thickness often is required in quantitative transmission electron microscopy. The methods used for thickness determinations of thin crystalline materials (e.g. the trace method, thickness fringe counts and stereoscopic measurements) generally are selected according to the history of the specimen and nature of the microstructure. For amorphous materials a measurement of the relative transmission of electrons I/I0, where I is the transmitted and I0 the incident electron intensity, affords an accurate estimate of the specimen thickness. In this case, for a sufficiently large specimen thickness, I/I0 varies exponentially according to the mass thickness relationship e-μt, where μ is the mass absorption coefficient and t is the specimen thickness. The purpose of this paper is to demonstrate that the thickness of a crystalline specimen also may be determined accurately from a measurement of I/I0, provided that well defined diffracting conditions are used. The results presented here are for silicon.

Techniques for structural studies of liquids and amorphous materials by neutron diffraction at high pressures and temperatures

2004 ◽  
Vol 24 (1) ◽  
pp. 205-217 ◽  
Author(s):  
Y. Le Godec ◽  
T. Strässle ◽  
G. Hamel ◽  
R. J. Nelmes ◽  
J. S. Loveday ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Amorphous Materials ◽  
High Pressures ◽  
Structural Studies ◽  
High Pressures And Temperatures
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