Crystal Structure Evolution of La2Ni7 during Hydrogenation

2013 ◽  
Vol 1516 ◽  
pp. 183-188 ◽  
Author(s):  
Yuki Iwatake ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Hydrogen Absorption ◽  
Dark Field ◽  
Atomic Scale ◽  
Structure Evolution ◽  
Desorption Process ◽  
Atomic Arrangement ◽  
Anisotropic Expansion ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Scale Characterization

ABSTRACTAtomic scale characterization of the La2Ni7 hydrides by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that not only the anisotropic expansion of the La2Ni4 unit layer previously reported but also the shearing on the basal plane of the La2Ni4 unit layers occur during one-cycle of hydrogen absorption/desorption process. Two different types of orthorhombic La2Ni7 hydrides with the same atomic arrangement of La and different atomic arrangement of Ni were observed depending on the maximum hydrogen concentration achieved during one hydrogen absorption/desorption cycle.

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.

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.

Growth and Overgrowth of Ge/Si Quantum Dots: An Observation by Atomic Resolution HAADF-STEM Imaging

2004 ◽  
Vol 832 ◽  
Author(s):  
Dan Zhi ◽  
Paul A. Midgley ◽  
Rafal E. Dunin-Borkowski ◽  
Bruce A. Joyce ◽  
Don W. Pashley ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Direct Analysis ◽  
Lateral Spreading ◽  
Dark Field ◽  
Atomic Scale ◽  
Wetting Layer ◽  
Compositional Evolution ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Self Assembled

ABSTRACTThe formation of self-assembled quantum dots (QD) is of increasing interest for applications in optical, nanoelectronic, biological and quantum computing systems. From the perspective of fabrication technology, there are great advantages if the whole device can be made using a single Si substrate. Furthermore, GeSi is a model semiconductor system for fundamental studies of growth and material properties. In practice, as the MBE growth of heterostructures is inherently a non-equilibrium process, the formation of self-assembled nanostructures is both complex and sensitive to growth and overgrowth conditions. The morphology, structure and composition of QDs can all change during growth. It is therefore crucial to understand their structures at different stages of growth at the atomic scale. Here, the characterization of QD growth using high-resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging is presented. Both the formation of uncapped QDs and the effect of the encapsulation are investigated, and the morphological and compositional evolution of the QDs and wetting layers are observed directly at the atomic scale for the first time. During encapsulation, the Ge content in the centres of the QD remains unchanged, despite significant intermixing, lateral spreading and a laterally inhomogeneous Ge distribution inside the Ge QD. The initial non-uniform wetting layer for the uncapped Ge QD becomes uniform after encapsulation, and a 3-monolayer-thick core with ∼ 60% Ge content is formed in the 2 nm-thick wetting layer with an average Ge content of ∼ 30%. The results were obtained by direct analysis of the Z-contrast STEM imaging without involving complex image simulations.

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 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.

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.

Atomic Scale Characterization of Vacancy Ordering in Oxygen Conducting Membranes

2002 ◽  
Vol 8 (6) ◽  
pp. 475-486 ◽  
Author(s):  
Robert F. Klie ◽  
Nigel D. Browning
Keyword(s):  
Defect Formation ◽  
Bulk Material ◽  
Electronic Conductivity ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Structure Property ◽  
Dark Field Imaging ◽  
Scanning Transmission ◽  
Scale Characterization

This article presents a comprehensive investigation of (La, Sr)FeO3 by correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy. Here, the ability of these techniques to characterize point defect formation and phase transitions under reducing conditions in situ in the scanning transmission electron microscope is evaluated and the influence of oxygen vacancies on the structure–property relationships is discussed. In particular, the evolution of the Ruddlesden–Popper, Brownmillerite, and Aurivillius phases can be associated directly with the ionic and electronic conductivity of the bulk material under different thermodynamic conditions. These results lead naturally to an atomistic defect chemistry model to explain the high temperature ionic and electronic conductivity in this and other perovskite materials.

Quantitative Strain Mapping Applied to Aberration-Corrected HAADF Images

2006 ◽  
Vol 12 (4) ◽  
pp. 285-294 ◽  
Author(s):  
Ana M. Sanchez ◽  
Pedro L. Galindo ◽  
Slawomir Kret ◽  
Meiken Falke ◽  
Richard Beanland ◽  
...  
Keyword(s):  
Quantitative Measure ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Internal Strain ◽  
Atomic Scale ◽  
Strain Mapping ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Free Material ◽  
Aberration Corrected

A systematic distortion in high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, which may be caused by residual electrical interference, has been evaluated. Strain mapping, using the geometric phase methodology, has been applied to images acquired in an aberration-corrected STEM. This allows this distortion to be removed and so quantitative analysis of HAADF-STEM images was enabled. The distortion is quantified by applying this technique to structurally perfect and strain-free material. As an example, the correction is used to analyse an InAs/GaAs dot-in-quantum well heterostructure grown by molecular beam epitaxy. The result is a quantitative measure of internal strain on an atomic scale. The measured internal strain field of the heterostructure can be interpreted as being due to variations of indium concentration in the quantum dot.

Atomic Scale Characterization Of Interfaces And Defects In Non-Stoichiometricmulticomponent Oxides

1999 ◽  
Vol 5 (S2) ◽  
pp. 106-107
Author(s):  
S. Stemmer ◽  
S. K. Streiffer ◽  
A. Sane ◽  
T. J. Mazanec ◽  
N. D. Browning
Keyword(s):  
Dark Field ◽  
Atomic Scale ◽  
Chemical Information ◽  
Structure Property ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Scale Characterization ◽  
Electron Microscopes

The ability to obtain chemical information with (near) atomic resolution has recently become possible by a combined approach of Z-contrast imaging with electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopes. This method is particularly interesting for the characterization of structure-property relationships in novel multicomponent oxides, which possess added functionality due to their high nonstoichiometry.In this paper we demonstrate the capabilities of this method in analyzing the microstructural mechanisms of accommodation of non-stoichiometry, using two example systems: (Ba,Sr)TiO3thin films for DRAM applications, grown by MOCVD with different amounts of excess titanium, and an oxygen-deficient perovskite ceramic, SrCoOx. The experiments were performed in a JEOL JEM 201 OF field emission transmission electron microscope, operating at 200 kV, equipped with an annular dark-field detector, scanning unit and a post-column imaging filter (Gatan GIF 200). This microscope has been demonstrated to achieve probe sizes of under 1.5 Å .

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