Quantitative HREM analysis of planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 720-721
Author(s):  
Hong Zhang ◽  
L. D. Marks ◽  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
...  
Keyword(s):  
High Pressure ◽  
Atomic Scale ◽  
Structure Model ◽  
Hrem Image ◽  
Ion Milling ◽  
Planar Defects ◽  
Infinite Layer ◽  
Transmission Electron ◽  
Best Fit ◽  
Image Simulations

Planar defects in the infinite-layer (Sr1-xCax)1-yCuO2 structure (planar CuO2 sheets separated by single Sr and Ca cations) have been suggested to be responsible for superconductivity with Tc up to about 110K. It is therefore important to understand the details of these defects at the atomic scale. In this work, we have used high resolution transmission electron microscopy to identify these defects and χ2 minimizations to best fit the experimental images; an optimized structure model from these studies is proposed.Thin samples of the infinite layer superconductor with the nominal chemical formula (Sr1-xCax)1-y CuO2 (x=0 and 0.3; y=0.9, 1.0 and 1.1) synthesized by high pressure treatment were prepared using a combination of mechanical polishing, dimpling and ion milling techniques. Through focal (10 nm steps) [100] HREM images of the defects (Fig. 1) were obtained on a 300kV Hitachi H-9000 microscope. HREM image simulations were carried out using NUMIS software and these were quantitatively compared against the experimental images using conventional χ2 minimizations with SEMPER software.

Microstructural Study of Diamond Deformed Under High Pressure and Temperature

1985 ◽  
Vol 43 ◽  
pp. 230-231
Author(s):  
E. F. Koch
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Lattice Structure ◽  
Diamond Particle ◽  
Polycrystalline Diamond ◽  
Sintering Process ◽  
Ion Milling ◽  
Sintered Compact ◽  
Transmission Electron ◽  
High Pressure Sintering

Because of the extremely rigid lattice structure of diamond, generating new dislocations or moving existing dislocations in diamond by applying mechanical stress at ambient temperature is very difficult. Analysis of portions of diamonds deformed under bending stress at elevated temperature has shown that diamond deforms plastically under suitable conditions and that its primary slip systems are on the ﹛111﹜ planes. Plastic deformation in diamond is more commonly observed during the high temperature - high pressure sintering process used to make diamond compacts. The pressure and temperature conditions in the sintering presses are sufficiently high that many diamond grains in the sintered compact show deformed microtructures.In this report commercially available polycrystalline diamond discs for rock cutting applications were analyzed to study the deformation substructures in the diamond grains using transmission electron microscopy. An individual diamond particle can be plastically deformed in a high pressure apparatus at high temperature, but it is nearly impossible to prepare such a particle for TEM observation, since any medium in which the diamond is mounted wears away faster than the diamond during ion milling and the diamond is lost.

Nano-probe x-ray analysis and high-resolution imaging on planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 728-729
Author(s):  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
H. Zhang ◽  
L. D. Marks ◽  
...  
Keyword(s):  
High Pressure ◽  
High Resolution ◽  
Atomic Structure ◽  
Emission Spectra ◽  
High Resolution Electron Microscopy ◽  
Planar Defects ◽  
X Ray ◽  
Infinite Layer ◽  
Resolution Electron ◽  
Resolution Imaging

Azuma et al. observed planar defects in a high pressure synthesized infinitelayer compound (i.e. ACuO2 (A=cation)), which exhibits superconductivity at ~110 K. It was proposed that the defects are cation deficient and that the superconductivity in this material is related to the planar defects. In this report, we present quantitative analysis of the planar defects utilizing nanometer probe xray microanalysis, high resolution electron microscopy, and image simulation to determine the chemical composition and atomic structure of the planar defects. We propose an atomic structure model for the planar defects.Infinite-layer samples with the nominal chemical formula, (Sr1-xCax)yCuO2 (x=0.3; y=0.9,1.0,1.1), were prepared using solid state synthesized low pressure forms of (Sr1-xCax)CuO2 with additions of CuO or (Sr1-xCax)2CuO3, followed by a high pressure treatment.Quantitative x-ray microanalysis, with a 1 nm probe, was performed using a cold field emission gun TEM (Hitachi HF-2000) equipped with an Oxford Pentafet thin-window x-ray detector. The probe was positioned on the planar defects, which has a 0.74 nm width, and x-ray emission spectra from the defects were compared with those obtained from vicinity regions.

Deformation-induced α2 ↔ γ phase transformation in a Ti–48Al–2Cr alloy

2000 ◽  
Vol 15 (10) ◽  
pp. 2145-2150 ◽  
Author(s):  
J. X. Zhang ◽  
H. Q. Ye
Keyword(s):  
Electron Microscopy ◽  
Phase Transformation ◽  
Lattice Misfit ◽  
Hrem Image ◽  
Shockley Partial ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Ledge Mechanism ◽  
Related Process ◽  
Image Simulations

The structure of γ–α2 interfaces in deformed Ti–48Al–2Cr alloy was analyzed by high-resolution transmission electron microscopy (HREM) and image simulations. Growth of γ–TiAl plate in α2–Ti3Al phase was found to be a result of a ledge mechanism consisting of Shockley partial dislocations on alternate (0001)α2 planes. The height of the ledges was always a multiple of two (0001)α2 planes. The γ → α2 phase transformation was also an interface-related process. Large ledges of six close packed planes (111)γ high were often observed at the γ–α2 interface. Every large ledge consisted of six Shockley partial dislocations that originated from the γ–a2 interfacial lattice misfit. The movement of these partial dislocations accomplished the transformation of γ → α2 phase. Comparing the experimental and simulated HREM image, it was found that atomic reordering appears during the deformation-induced γ↔α2 transformation.

Complex Defect in Pyrite and Its Structure Model Derived from Geometric Phase Analysis

2013 ◽  
Vol 19 (5) ◽  
pp. 1303-1307 ◽  
Author(s):  
Péter Németh ◽  
István Dódony ◽  
Mihály Pósfai ◽  
Peter R. Buseck
Keyword(s):  
Phase Analysis ◽  
Geometric Phase ◽  
Atomic Scale ◽  
Structure Model ◽  
Hrtem Image ◽  
New Methods ◽  
Transmission Electron ◽  
Geometric Phase Analysis ◽  
High Resolution Tem ◽  
Line Dislocation

AbstractNew methods for defect analysis can lead to improved interpretation of experimental data and thus better understanding of material properties. Although transmission electron microscopy (TEM) has been used to study defects for many decades, interpretive ambiguities can arise for cases that seem simple or even trivial. Using geometric phase analysis (GPA), an image processing procedure, we show that an apparent simple line defect in pyrite has an entirely different character. It appears to be a b = ½[100] edge dislocation as viewed in a [001] high-resolution TEM (HRTEM) image, but the measured ux and uy displacements are asymmetric, which is inconsistent with a simple line dislocation. Instead, the defect is best understood as a terminating {101} marcasite slab in pyrite. The simulated HRTEM image based on this model reproduces the defect contrast and illustrates the power of GPA analysis for (1) avoiding potential pitfalls of misinterpreting apparently simple defects in HRTEM images, (2) detecting differences in elastic properties at the atomic scale, and (3) providing data for the positions of atom columns, thereby facilitating the construction of structure models for complex defects.

scholarly journals STEM-EELS Investigation of Planar Defects in Olivine in the Allende Meteorite

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 35
Author(s):  
Maya Marinova ◽  
Hugues Leroux ◽  
Priscille Cuvillier ◽  
Alexandre Gloter ◽  
Damien Jacob
Keyword(s):  
Structural Features ◽  
Dark Field ◽  
Parent Body ◽  
Atomic Scale ◽  
Crystalline Lattice ◽  
Planar Defects ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Small Distortion

The present study focuses on a detailed structural investigation at atomic scale of the planar defects that appear in the olivine grains in the Allende meteorite, and it aims to clarify their nature and the related formation mechanism. The investigation was performed using advanced spectro-microscopy techniques such as atomically resolved high-angle annular dark field (HAADF) images coupled with electron energy loss spectroscopy in the scanning transmission electron microscopy mode (STEM-EELS). Two prominent structural features appear in the investigated olivine grains: (i) Exsolution platelets with a thickness between 2 and 10 nm with the spinel structure and chemical composition expressed as a solid solution between magnetite, chromite, and MgAl2O4. (ii) Thinner planar defects appeared with thickness between 2 to 4 atomic planes, which were rich in Fe and had a strong Fe3+ contribution. The structure of these defects was described by the crystalline lattice of the olivine grains with small distortion of the measured cationic distances, which can be related to Fe3+-Si substitution in the tetrahedral sites. Those metastable defects should have preceded the formation of the thicker spinel exsolutions and could have formed during an oxidizing event in the Allende parent body.

scholarly journals Defect-driven selective metal oxidation at atomic scale

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qi Zhu ◽  
Zhiliang Pan ◽  
Zhiyu Zhao ◽  
Guang Cao ◽  
Langli Luo ◽  
...  
Keyword(s):  
Reaction Dynamics ◽  
Binding Energies ◽  
Crystal Defects ◽  
Oxidation Catalysis ◽  
Atomic Scale ◽  
Layer By Layer ◽  
Oxygen Binding ◽  
Planar Defects ◽  
Transmission Electron ◽  
Site Selective

AbstractNanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned silver and palladium driven by individual stacking-faults and twin boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Planar-fault mediated diffusion of oxygen atoms is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by planar defects in metallic nanostructures, which could enable the modification of physiochemical performances in nanomaterials through defect engineering.

scholarly journals Where Is the Unmatched Transition Metal in Substoichiometric Diboride Line Compounds?

2020 ◽  
Author(s):  
Justinas Palisaitis ◽  
Martin Dahlqvist ◽  
Allen J. Hall ◽  
Jimmy Thörnberg ◽  
Ingemar Persson ◽  
...  
Keyword(s):  
Density Functional ◽  
Functional Theory ◽  
Local Composition ◽  
Planar Defects ◽  
Unbalanced Magnetron Sputtering ◽  
Transmission Electron ◽  
Unbalanced Magnetron ◽  
Scanning Transmission ◽  
Line Compound ◽  
Image Simulations

<div>The atomic structure and local composition of high quality epitaxial substoichiometric titanium</div><div>diboride (TiB<sub>1.9</sub>) thin film, deposited by unbalanced magnetron sputtering, were studied using</div><div>analytical high-resolution scanning transmission electron microscopy, density functional theory</div><div>and image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismatic</div><div>planes and attributed to the absence of B between Ti planes that locally relaxes the structure.</div><div>This mechanism allows the line compound to accommodate the off-stoichiometry and remain</div><div>a line compound between defects. The planar defects are embedded in otherwise stoichiometric</div><div>TiB<sub>2</sub> and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond</div><div>lengths along and across the faults is observed.</div><div>Introduction</div>

Where Is the Unmatched Transition Metal in Substoichiometric Diboride Line Compounds?

2020 ◽  
Author(s):  
Justinas Palisaitis ◽  
Martin Dahlqvist ◽  
Allen J. Hall ◽  
Jimmy Thörnberg ◽  
Ingemar Persson ◽  
...  
Keyword(s):  
Density Functional ◽  
Functional Theory ◽  
Local Composition ◽  
Planar Defects ◽  
Unbalanced Magnetron Sputtering ◽  
Transmission Electron ◽  
Unbalanced Magnetron ◽  
Scanning Transmission ◽  
Line Compound ◽  
Image Simulations

<div>The atomic structure and local composition of high quality epitaxial substoichiometric titanium</div><div>diboride (TiB<sub>1.9</sub>) thin film, deposited by unbalanced magnetron sputtering, were studied using</div><div>analytical high-resolution scanning transmission electron microscopy, density functional theory</div><div>and image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismatic</div><div>planes and attributed to the absence of B between Ti planes that locally relaxes the structure.</div><div>This mechanism allows the line compound to accommodate the off-stoichiometry and remain</div><div>a line compound between defects. The planar defects are embedded in otherwise stoichiometric</div><div>TiB<sub>2</sub> and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond</div><div>lengths along and across the faults is observed.</div><div>Introduction</div>

Microstructural characterization of YBa2Cu3O7−x

1987 ◽  
Vol 2 (6) ◽  
pp. 736-742 ◽  
Author(s):  
M. Sarikaya ◽  
B. L. Thiel ◽  
I. A. Aksay ◽  
W. J. Weber ◽  
W. S. Frydrych
Keyword(s):  
Microstructural Characterization ◽  
Laser Raman Spectroscopy ◽  
Ion Milling ◽  
Detailed Characterization ◽  
Planar Defects ◽  
Resistivity Measurements ◽  
Laser Raman ◽  
Transmission Electron ◽  
Characterization Study

A detailed characterization study on polycrystalline specimens of YBa2Cu3Oy-x that were prepared by solid-state reaction techniques has been carried out. In the samples studied. magnetization and resistivity measurements indicate superconductivity onset temperatures of up to 89 K. Transmission electron microscopy (TEM) techniques have been used to facilitate direct microstructural characterization. It is shown that the planar defects on (001) planes form during the ion milling of the samples and are not directly connected with superconductivity. Laser Raman spectroscopy has revealed that these materials are sensitive to environmental degradation.

Simulating the fine structure in HRTEM images of defects

1990 ◽  
Vol 48 (4) ◽  
pp. 448-449
Author(s):  
M. J. Mills
Keyword(s):  
Structural Information ◽  
Memory Capacity ◽  
Atomic Scale ◽  
Formation Theory ◽  
Crystalline Defects ◽  
Essential Step ◽  
Transmission Electron ◽  
Properties Of Materials ◽  
Image Simulations ◽  
Image Formation Theory

The macroscopic properties of materials are often determined by the atomic structure of crystalline defects. High resolution transmission electron microscopy (HRTEM) enables the study of internal defects on the atomic scale. Image simulations represent an essential step in these studies since it is generally not possible to deduce the atomic positions near defects directly from the image intensities. Fortunately, image simulations which employ the multislice method and incorporate image formation theory for partially coherent illumination offer an accurate means of simulating images. With the availability of faster computers with larger memory capacity, the routine calulation of images of aperiodic defects is now feasible. This discussion will focus on the use of image simulations to extract structural information at defects, and to account for the artifacts which are frequently encountered in these studies.

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