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.

Atomic-scale structural and compositional analyses of Ruddlesden-Popper planar faults in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics

2009 ◽  
Vol 24 (8) ◽  
pp. 2596-2604 ◽  
Author(s):  
Sašo Šturm ◽  
Makoto Shiojiri ◽  
Miran Čeh
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Transmission Electron ◽  
Initial Stage ◽  
Final Microstructure ◽  
Scanning Transmission ◽  
The Matrix ◽  
Annular Dark Field

The microstructure in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics is strongly affected by the formation of Ruddlesden-Popper fault–rich (RP fault) lamellae, which are coherently intergrown with the matrix of the perovskite grains. We studied the structure and chemistry of RP faults by applying quantitative high-resolution transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy analyses. We showed that the Sr2+ and Ca2+ dopant ions form RP faults during the initial stage of sintering. The final microstructure showed preferentially grown RP fault lamellae embedded in the central part of the anisotropic perovskite grains. In contrast, the dopant Ba2+ ions preferably substituted for Sr2+ in the SrTiO3 matrix by forming a BaxSr1−xTiO3 solid solution. The surplus of Sr2+ ions was compensated structurally in the later stages of sintering by the formation of SrO-rich RP faults. The resulting microstructure showed RP fault lamellae located at the surface of equiaxed BaxSr1-xTiO3 perovskite grains.

Microstructure and ferroelectric properties of ultrathin PbTiO3 films by MOCVD

2005 ◽  
Vol 902 ◽  
Author(s):  
Hironori Fujisawa ◽  
Toru Horii ◽  
Yoshiyuki Takashima ◽  
Masaru Shimizu ◽  
Yasutoshi Kotaka ◽  
...  
Keyword(s):  
Ferroelectric Properties ◽  
Piezoresponse Force Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Epitaxial Relationship ◽  
X Ray ◽  
Force Microscopy ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

AbstractWe report on microstructure and ferroelectric properties of ultrathin PbTiO3 films epitaxially grown on SrTiO3(100), La-doped SrTiO3(100) and SrRuO3/SrTiO3(100) by MOCVD. High angle annular dark field scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction and x-ray reflectivity measurements demonstrated that 1-20 monolayer (ML)-thick epitaxial PbTiO3 films had high-crystallinity, atomically flat surface and sharp interface at an atomic scale. The epitaxial relationship and thickness were also confirmed by these methods. Kelvin force probe microscopy and contact resonance piezoresponse force microscopy revealed that a 7ML (2.7nm)-thick PbTiO3 film grown on SrRuO3/SrTiO3 had the ferroelectric polarization.

scholarly journals Atomic-Scale Characterization of Commensurate and Incommensurate Vacancy Superstructures in Natural Pyrrhotites

2021 ◽  
Vol 106 (1) ◽  
pp. 82-96 ◽  
Author(s):  
Lei Jin ◽  
Dimitrios Koulialias ◽  
Michael Schnedler ◽  
Andreas U. Gehring ◽  
Mihály Pósfai ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Past Century ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Local Measurements ◽  
Scale Characterization

Abstract Pyrrhotites, characterized by the chemical formula Fe1–δS (0 < δ ≤ 1/8), represent an extended group of minerals that are derived from the NiAs-type FeS aristotype. They contain layered arrangements of ordered Fe vacancies, which are at the origin of the various magnetic signals registered from certain natural rocks and can act as efficient electrocatalysts in oxygen evolution reactions in ultrathin form. Despite extensive studies over the past century, the local structural details of pyrrhotite superstructures formed by different arrangements of Fe vacancies remain unclear, in particular at the atomic scale. Here, atomic-resolution high-angle annular dark-field imaging and nanobeam electron diffraction in the scanning transmission electron microscope are used to study natural pyrrhotite samples that contain commensurate 4C and incommensurate 4.91 ± 0.02C constituents. Local measurements of both the intensities and the picometer-scale shifts of individual Fe atomic columns are shown to be consistent with a model for the structure of 4C pyrrhotite, which was derived using X-ray diffraction by Tokonami et al. (1972). In 4.91 ± 0.02C pyrrhotite, 5C-like unequally sized nano-regions are found to join at anti-phase-like boundaries, leading to the incommensurability observed in the present pyrrhotite sample. This conclusion is supported by computer simulations. The local magnetic properties of each phase are inferred from the measurements. A discussion of perspectives for the quantitative counting of Fe vacancies at the atomic scale is presented.

Nano-Sized Cuboid-Shaped Phase in Mg–Nd–Y Alloy and its Behavior During Isothermal Aging

2016 ◽  
Vol 22 (6) ◽  
pp. 1244-1250 ◽  
Author(s):  
Jingxu Zheng ◽  
Zhongyuan Luo ◽  
Lida Tan ◽  
Bin Chen
Keyword(s):  
Isothermal Aging ◽  
Lattice Parameter ◽  
Dark Field ◽  
Atomic Scale ◽  
Face Centered Cubic ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Face Centered ◽  
Image Position

AbstractIn the present study, nano-sized cuboid-shaped particles in Mg–Nd–Y are studied by means of Cs-corrected atomic-scale high-angle annular dark-field scanning transmission electron microscopy. The structure of the cuboid-shaped phase is identified to be yttrium (major component) and neodymium atoms in face-centered cubic arrangement without the participation of Mg. The lattice parameter a=5.15 Å. During isothermal aging at 225°C, Mg3(Nd,Y) precipitates adhere to surface (100) planes of the cuboid-shaped particles with the orientation relationship: $[100]_{{{\rm Mg}_{{\rm 3}} {\rm RE}}} \,/\,\,/\,[100]_{{{\rm Cuboid}}} $ and $[310]_{{{\rm Mg}_{{\rm 3}} {\rm RE}}} \,/\,\,/\,[012]_{{{\rm Cuboid}}} $ . The fully coherent interfaces between the precipitates and the cuboid-shaped phases are reconstructed and categorized into two types: $(400)_{{{\rm Mg}_{{\rm 3}} {\rm RE}}} $ interface and $(200)_{{{\rm Mg}_{{\rm 3}} {\rm RE}}} $ interface.

scholarly journals Effect of Micro-Steps on Twinning and Interfacial Segregation in Mg-Ag Alloy

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1307 ◽  
Author(s):  
Yi Liu ◽  
Xuefei Chen ◽  
Kang Wei ◽  
Lirong Xiao ◽  
Bin Chen ◽  
...  
Keyword(s):  
Twin Boundary ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Misfit Dislocations ◽  
Twin Boundaries ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Interfacial Segregation

Twinning structures and their interfacial segregation play a key role in strengthening of magnesium alloys. Micro-steps are frequently existed in the incoherent twin boundaries, while the effect of them on interface and interfacial segregation is still not clear. In this work, we performed an atomic-scale microstructure analysis using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to explore the effect of micro-steps on twin and its interfacial segregation in Mg-Ag alloy. Diffraction pattern of the incoherent {10 1 ¯ 1} twin shows that the misorientation has a slight tilt of 5° from its theoretical angle of 125° due to the accumulated effects of the micro-steps and their misfit dislocations in twin boundaries. Most of the micro-steps in {10 1 ¯ 1} twin boundary are in the height of 2 d ( 10 1 ¯ 1 ) and 4 d ( 10 1 ¯ 1 ) , respectively, and both of them have two types according to whether there are dislocations on the micro-steps. The twin boundary is interrupted by many micro-steps, which leads to a step-line distributed interfacial segregation. Moreover, the Ag tends to segregate to dislocation cores, which results in the interruption of interfacial segregation at the micro-steps with dislocations.

Atomic Scale Grain Boundary Analysis by Incoherent Imaging With TEM/STEM

2000 ◽  
Vol 6 (S2) ◽  
pp. 124-125
Author(s):  
M. Kawasaki ◽  
T. Yamazaki ◽  
K. Watanabe ◽  
M. Shiojiri
Keyword(s):  
Grain Boundary ◽  
Boundary Region ◽  
Dark Field ◽  
Atomic Scale ◽  
Image Simulation ◽  
Diffusion Layers ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Incoherent Imaging

Quantitative compositional characterization was carried out on a ceramic boundary using atomic resolution high-angle annular dark field scanning transmission electron microscopy (HAADFSTEM), with the aid of HAADF image simulation. HAADF-STEM observation was performed with a JEM-2010F TEM/STEM equipped with a field emission gun and an HAADF detector. And also the image simulation for HAADF was made on a computer by the program that was developed by the authors using Bethe's method.The material used in this experiment that was provided by TDK Co., is a semiconducting SrTiO3 (STO) ceramic condenser. The bulk substance was formed by the process of sintering in a reduced ambience followed by the reoxidization in the air after surface coating with Bi2O3, PbO and CuO compounds resulting in having a unique structure with Bi diffusion layers at the grain boundary region.

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

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