Dislocations and related defects in niobium oxide structures

1977 ◽  
Vol 352 (1670) ◽  
pp. 303-323 ◽  
Keyword(s):  
Chemical Composition ◽  
Niobium Oxide ◽  
Shear Plane ◽  
Extended Defects ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Lattice Images ◽  
Crystallographic Shear ◽  
Third Dimension ◽  
Block Structures

Lattice images of the niobium oxides, structures based on the linkage of octahedral groups in continuous networks, occasionally contain features recognizable as dislocations. Since lattice imaging enables the micro-structure to be resolved in great detail, at the level of local structural organization, it is possible to determine the configuration, and also to infer the chemical composition, of dislocated areas. By treating the niobium oxide ‘block’ structures as superstructures of the ReO 3 (DO 9 ) type, the topology of dislocations can be expressed by relations between the insertion (or deletion) of one or more half-planes of cations, or of oxygen atoms only, changes in the number of crystallographic shear plane interfaces between blocks or columns, changes in (idealized) dimensions and any requisite distortion in the third dimension. Mapping the structure around a dislocation, from the lattice image, is directly equivalent to plotting the Burgers’ circuit. In this way, the precise nature of a dislocating perturbation and its implications for the local chemical composition of the crystal can be directly identified. The method is exemplified by analysis of dislocations and of related extended defects of several types, associated with twinning phenomena, semicoherent intergrowth between different ReO 3 -type superstructures and arrays building up a low angle boundary. The essential features of the analysis are not restricted to structures of the niobium oxide type, but can be extended to other types of polyhedron networks.

Mapping the composition of materials at the atomic level

1992 ◽  
Vol 50 (2) ◽  
pp. 1474-1475
Author(s):  
A. Ourmazd ◽  
F.H. Baumann ◽  
Y. Kim ◽  
C. Kisielowski ◽  
P. Schwander
Keyword(s):  
Imaging Techniques ◽  
Atomic Level ◽  
Objective Lens ◽  
Lattice Imaging ◽  
Electron Microscopic ◽  
Lattice Image ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Lattice Images ◽  
Compositional Changes

This paper briefly outlines how transmission electron microscopic lattice imaging techniques can be used to map the composition of crystalline materials at the atomic level.Under appropriate conditions, a conventional lattice image is a map of the sample structure, because the dominant reflections used to form lattice images are relatively insensitive to compositional changes in the sample. Such reflections may be termed “structural”. In many cystalline materials, compositional changes occur by atomic substitution on a particular subset of lattice sites. In these systems, compositional changes are accompanied by the appearance of reflections, which we name “chemical”. Such reflections, for example the (200) in the zinc-blende structure, owe their existence to chemical differences between the various atomic species present on the different lattice sites. For fundamental reasons these reflections are often weak; they come about because of incomplete cancellation of out of phase contributions from different sublattices. “Chemical lattice imaging” exploits dynamical scattering to maximize the intensity of such reflections, and uses the objective lens as a bandpass filter to enhance their contribution to the image.

The structure of germanium niobium oxide, an inherently non-stoichiometric ‘block’ structure

1975 ◽  
Vol 346 (1645) ◽  
pp. 139-156 ◽  
Keyword(s):  
Niobium Oxide ◽  
Profile Analysis ◽  
Extended Defects ◽  
X Ray Diffraction ◽  
Anion Sublattice ◽  
Lattice Imaging ◽  
High Concentration ◽  
Metal Atoms ◽  
Distorted Octahedral ◽  
Cation Sites

Germanium niobium oxide, reported as Ge02. 9Nb20 5, is inherently nonstoichiometric since it appears to be isostructural with P 20 5. 9Nb20 5. To fit this structure, there must be vacant oxygen sites or some sites accommodating ‘interstitial’ metal atoms, in relatively high concentration, and the mode of incorporating a stoichiometric excess of cations should cast some light on other niobium oxide type structures which have a reported range of composition. The structure of germanium niobium oxide has been determined by a combination of three methods: lattice imaging electron microscopy, to establish that the non-stoichiometry was not attributable to extended defects; neutron diffraction, using the powder method and profile analysis, for particular evidence about the anion sublattice and distribution of cations; and X-ray diffraction, for an ab initio refined structure. It has been proved that the anion lattice is essentially complete, and that the cation excess is accommodated by inserting cations into a set of sites, with distorted octahedral coordination, in the square tunnels formed by the junctions between columnar elements of structure. Occupation of these octahedral sites precludes the occupation of adjacent tetrahedral cation sites, proper to the type structure. In consequence, there are constraints on the way that the two kinds of tunnel site can be occupied to produce the observed stoichiometric excess of cations. The resulting model can be generalized to interpret the metal-excess composition ranges found for other niobium oxide structures.

Chemical mapping of materials at the atomic level

1991 ◽  
Vol 49 ◽  
pp. 844-845
Author(s):  
A. Ourmazd ◽  
F. Baumann ◽  
M. Bode ◽  
Y. Kim ◽  
J.L. Rouviere
Keyword(s):  
Bandpass Filter ◽  
Objective Lens ◽  
Chemical Mapping ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Zinc Blende ◽  
Lattice Images ◽  
Sample Structure ◽  
Compositional Changes ◽  
Zinc Blende Structure

Under appropriate conditions, a conventional lattice image is a map of the sample structure, because the dominant reflections used to form lattice images are relatively insensitive to compositional changes in the sample. However, certain reflections, such as the (200) in the zinc-blende structure, owe their existence to chemical differences between the various atomic species present on the lattice sites. Such chemical reflections arc sensitive to compositional changes in the sample. For fundamental reasons such reflections are often weak; they come about because of incomplete cancellation of out of phase contributions from different sublattices. “Chemical lattice imaging” exploits dynamical scattering to maximize the intensity of such reflections, and uses the objective lens as a bandpass filter to enhance their contribution to the image.

Lattice Imaging of Twin, Lath and α/Martensite Boundaries in Duplex Low Carbon Steels

1977 ◽  
Vol 35 ◽  
pp. 118-119
Author(s):  
J. Y. Koo ◽  
G. Thomas
Keyword(s):  
High Resolution Electron Microscopy ◽  
Ferrite Matrix ◽  
Carbon Steels ◽  
Bright Field Image ◽  
Low Carbon ◽  
Lattice Imaging ◽  
Bright Field ◽  
Lattice Image ◽  
New Information ◽  
Resolution Electron

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

Microstructural Evolution in Reduced TiO2

1981 ◽  
Vol 39 ◽  
pp. 74-75
Author(s):  
W. T. Donlon ◽  
S. Shinozaki ◽  
E. M. Logothetis ◽  
W. Kaizer
Keyword(s):  
Microstructural Evolution ◽  
Point Defects ◽  
Extended Defects ◽  
Small Deviations ◽  
Controlled Atmospheres ◽  
Limited Solubility ◽  
Thin Foils ◽  
Heat Treated ◽  
Porous Polycrystalline ◽  
Crystallographic Shear

Since point defects have a limited solubility in the rutile (TiO2) lattice, small deviations from stoichiometry are known to produce crystallographic shear (CS) planes which accomodate local variations in composition. The material used in this study was porous polycrystalline TiO2 (60% dense), in the form of 3mm. diameter disks, 1mm thick. Samples were mechanically polished, ion-milled by conventional techniques, and initially examined with the use of a Siemens EM102. The electron transparent thin foils were then heat-treated under controlled atmospheres of CO/CO2 and H2 and reexamined in the same manner.The “as-received” material contained mostly TiO2 grains (∼5μm diameter) which had no extended defects. Several grains however, aid exhibit a structure similar to micro-twinned grains observed in reduced rutile. Lattice fringe images (Fig. 1) of these grains reveal that the adjoining layers are not simply twin related variants of a single TinO2n-1 compound. Rather these layers (100 - 250 Å wide) are alternately comprised of stoichiometric TiO2 (rutile) and reduced TiO2 in the form of Ti8O15, with the Ti8O15 layers on either side of the TiO2 being twin related.

7-beam lattice images of (110) oriented Ge

1978 ◽  
Vol 36 (1) ◽  
pp. 290-291
Author(s):  
J.R. Parsons ◽  
C.W. Hoelke
Keyword(s):  
Image Features ◽  
Objective Lens ◽  
Lattice Plane ◽  
Lattice Image ◽  
Crystalline Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Structural Aspects ◽  
Beam Lattice

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.

The ultrastructure of coccoliths from the marine alga Emiliania huxleyi (Lohmann) Hay and Mohler: an ultra-high resolution electron microscope study

1983 ◽  
Vol 219 (1215) ◽  
pp. 111-117 ◽  
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Emiliania Huxleyi ◽  
Growth Patterns ◽  
Lattice Image ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Lattice Images ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns

The calcite coccoliths from the alga Emiliania huxleyi (Lohmann) Hay and Mohler have been studied by ultra-high resolution electron microscopy. This paper describes the two different types of structure observed, one in the upper elements, the other in the basal plate, or lower element. The former consisted of small, microdomain structures of 300-500 Å (1 Å = 10 -10 m) in length with no strong orientation. At places along these elements, and particularly in the junction between stem and head pieces, triangular patterns of lattice fringes were observed indicating multiple nucleation sites in the structure. In contrast, the lower element consisted of a very thin single crystalline sheet of calcite which could be resolved into a two dimensional lattice image, shown by a computer program that is capable of simulating electron diffraction patterns and lattice images to be a [421] zone of calcite. A possible mechanism for these growth patterns in the formation of coccoliths is discussed, together with the relevance of such mechanisms to biomineralization generally.

The Structure of the (001)Si/SiO2 Interface

1987 ◽  
Vol 105 ◽  
Author(s):  
A. Ourmazd ◽  
J. Bevk
Keyword(s):  
Electron Diffraction ◽  
Structural Data ◽  
Bulk Phase ◽  
Careful Examination ◽  
Imaging Data ◽  
Lattice Imaging ◽  
Crystalline Layer ◽  
Crystalline Oxide ◽  
Lattice Images

AbstractWe show that a careful examination of previous microscopic structural data from the Si/SiO2 interface reveals that the presence of an epitaxial interfacial oxide cannot be ruled out, and describe the conditions necessary for a definitive search for an intervening layer between c-Si and a-SiO2 We present electron diffraction and lattice imaging data, which establish the c-Si→a-SiO2 transition to take place via a crystalline layer ˜7 A thick. Modelling of lattice images in two projections indicates the crystalline oxide to be tridymite, a stable, bulk phase of SiO2

Quantitative Hrtem: Measuring Projected Potential, Surface Roughness and Chemical Composition

1994 ◽  
Vol 332 ◽  
Author(s):  
P. Schwander ◽  
C. Kisielowski ◽  
F.H. Baumann ◽  
Y.O. Kim ◽  
A. Ourmazd
Keyword(s):  
Surface Roughness ◽  
Chemical Composition ◽  
Quantum Well ◽  
Cross Section ◽  
Potential Surface ◽  
Atomic Level ◽  
Topographic Map ◽  
Plan View ◽  
Lattice Images ◽  
Imaging Conditions

ABSTRACTWe describe how general lattice images may be used to measure the variation of the potential in crystalline solids in any projection, with no knowledge of the imaging conditions. This approach is applicable to structurally perfect samples, in which interfacial topography, or changes in composition are of interest. We present the first atomic-level topographic map of a Si/SiO2 interface in plan-view, and the first microscopic compositional map of a Si/GeSi/Si quantum well in cross-section.

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