Hidden order in amorphous structures: Extraction of nearest neighbor networks of amorphous Nd–Fe alloys with Gabriel graph analyses

Recently Cohen has predicted, based on an empirical model, that tetrahedral solids of low ionicity with high bulk moduli approaching that of diamond may be candidates as new hard materials. Several groups have attempted to synthesize these covalent C-N solids using vacuum deposition techniques. Although many of the literature results give C-N compounds with amorphous structures, two groups have reported the presence of a few percent of a crystalline phase, the so-called β-C3N4, after β-Si3N4 (hex.) structure, in an otherwise amorphous matrix. It has generally been difficult to synthesize samples with higher crystalline phase content and to confirm these early results. In samples prepared by a chemical precursor route, we report the presence of a crystalline carbonitride phase with zinc blende structure from electron diffraction and spectroscopy investigation. Based on a scaling relationship from Cohen, we estimate the bulk modulus of the new crystalline compound (denoted as α-C4N4 heretofore) to be comparable to c-BN and diamond from the C - N bond length determined from extended energy loss fine structure analysis, EXELFS, that allows a precise measurement of the first and second nearest neighbor distances between C and N atoms.

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Observation of Superlattice Dislocations on Cube Planes in Ni3Al

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071314 ◽

1973 ◽

Vol 31 ◽

pp. 174-175 ◽

Cited By ~ 1

Author(s):

J. M. Oblak ◽

W. H. Rand

Keyword(s):

Nearest Neighbor ◽

Antiphase Boundary ◽

Nearest Neighbors ◽

High Energy ◽

Cross Slip ◽

Octahedral Plane ◽

Trapping Mechanism ◽

Slip Traces

The energy of an a/2 <110> shear antiphase. boundary in the Ll2 expected to be at a minimum on {100} cube planes because here strue ture is there is no violation of nearest-neighbor order. The latter however does involve the disruption of second nearest neighbors. It has been suggested that cross slip of paired a/2 <110> dislocations from octahedral onto cube planes is an important dislocation trapping mechanism in Ni3Al; furthermore, slip traces consistent with cube slip are observed above 920°K.Due to the high energy of the {111} antiphase boundary (> 200 mJ/m2), paired a/2 <110> dislocations are tightly constricted on the octahedral plane and cannot be individually resolved.

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TEM studies of amorphization processes and amorphous structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104303 ◽

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.

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Application of Lattice Imaging Techniques to Amorphous Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113664 ◽

1975 ◽

Vol 33 ◽

pp. 8-9

Author(s):

S. R. Herd ◽

P. Chaudhari

Keyword(s):

Nearest Neighbor ◽

Random Network ◽

Imaging Techniques ◽

Network Models ◽

Accurate Method ◽

Direct Transmission ◽

Lattice Imaging ◽

Transmission Electron ◽

Lattice Planes ◽

Nearest Neighbor Distances

Electron diffraction and direct transmission have been used extensively to study the local atomic arrangement in amorphous solids and in particular Ge. Nearest neighbor distances had been calculated from E.D. profiles and the results have been interpreted in terms of the microcrystalline or the random network models. Direct transmission electron microscopy appears the most direct and accurate method to resolve this issue since the spacial resolution of the better instruments are of the order of 3Å. In particular the tilted beam interference method is used regularly to show fringes corresponding to 1.5 to 3Å lattice planes in crystals as resolution tests.

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Automated electron tomography: from data collection to image processing

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136507 ◽

1995 ◽

Vol 53 ◽

pp. 26-27

Author(s):

Weiping Liu ◽

Jennifer Fung ◽

W.J. de Ruijter ◽

Hans Chen ◽

John W. Sedat ◽

...

Keyword(s):

Image Processing ◽

Data Collection ◽

Structural Information ◽

Imaging Technique ◽

Electron Tomography ◽

Ccd Camera ◽

Automated Data Collection ◽

Full Control ◽

Transmission Electron ◽

Amorphous Structures

Electron tomography is a technique where many projections of an object are collected from the transmission electron microscope (TEM), and are then used to reconstruct the object in its entirety, allowing internal structure to be viewed. As vital as is the 3-D structural information and with no other 3-D imaging technique to compete in its resolution range, electron tomography of amorphous structures has been exercised only sporadically over the last ten years. Its general lack of popularity can be attributed to the tediousness of the entire process starting from the data collection, image processing for reconstruction, and extending to the 3-D image analysis. We have been investing effort to automate all aspects of electron tomography. Our systems of data collection and tomographic image processing will be briefly described.To date, we have developed a second generation automated data collection system based on an SGI workstation (Fig. 1) (The previous version used a micro VAX). The computer takes full control of the microscope operations with its graphical menu driven environment. This is made possible by the direct digital recording of images using the CCD camera.

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Structural studies of small amorphous volumes by electron diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173741 ◽

1990 ◽

Vol 48 (4) ◽

pp. 122-123

Author(s):

Pierre Moine

Keyword(s):

Electron Diffraction ◽

Born Approximation ◽

Structural Information ◽

Fundamental Relation ◽

X Rays ◽

Structural Studies ◽

Diffraction Experiment ◽

Transmission Electron ◽

Amorphous Structures ◽

Diffraction Patterns

Qualitatively, amorphous structures can be easily revealed and differentiated from crystalline phases by their Transmission Electron Microscopy (TEM) images and their diffraction patterns (fig.1 and 2) but, for quantitative structural information, electron diffraction pattern intensity analyses are necessary. The parameters describing the structure of an amorphous specimen have been introduced in the context of scattering experiments which have been, so far, the most used techniques to obtain structural information in the form of statistical averages. When only small amorphous volumes (< 1/μm in size or thickness) are available, the much higher scattering of electrons (compared to neutrons or x rays) makes, despite its drawbacks, electron diffraction extremely valuable and often the only feasible technique.In a diffraction experiment, the intensity IN (Q) of a radiation, elastically scattered by N atoms of a sample, is measured and related to the atomic structure, using the fundamental relation (Born approximation) : IN(Q) = |FT[U(r)]|.

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