Ferroelectric and Structural Antiphase Domains in Hexagonal RMnO3

2012 ◽  
Vol 1397 ◽  
Author(s):  
K. Kobayashi ◽  
T. Koyama ◽  
Y. Horibe ◽  
T. Katsufuji ◽  
S-W. Cheong ◽  
...  
Keyword(s):  
High Resolution ◽  
Ferroelectric Phase ◽  
Antiphase Domain ◽  
Antiphase Boundaries ◽  
Domain Structures ◽  
Domain Configuration ◽  
Lattice Images ◽  
Antiphase Domains ◽  
Diffraction Patterns ◽  
Characteristic Domain

ABSTRACTWe have investigated characteristic ferroelectric and structural antiphase domain structures in single crystals of hexagonal RMnO3 (R=Y, Ho, Lu, and Yb) by obtaining various electron diffraction patterns, dark-filed images and high-resolution lattice images. In the ferroelectric phase of RMnO3 characteristic domain structures consisting of six ferroelectric and structural antiphase domains, which can be identified as the “cloverleaf” pattern, is found in the (110) plane, in addition to the (001) plane, and are inherent to the ferroelectric phase of hexagonal RMnO3. In domain configuration with the cloverleaf pattern in the (110) plane, the structural antiphase boundaries are inclined to be parallel to the [001] direction.

Direct imaging of order-disorder and antiphase domain structures in Ti3Al intermetallic compound

1990 ◽  
Vol 48 (4) ◽  
pp. 480-481
Author(s):  
H. Q. Ye ◽  
T.S. Xie ◽  
D. Li
Keyword(s):  
Intermetallic Compound ◽  
Volume Fraction ◽  
Fundamental Problem ◽  
Antiphase Domain ◽  
Atomic Scale ◽  
Orientation Relationships ◽  
Domain Structures ◽  
Α Phase ◽  
Diffraction Patterns ◽  
Two Phases

The Ti3Al intermetallic compound has long been recognized as potentially useful structural materials. It offers attractive strength to weight and elastic modulus to weight ratios. Recent work has established that the addition of Nb to Ti3Al ductilized this compound. In this work the fundamental problem of this alloy, i.e. order-disorder and antiphase domain structures was investigated at the atomic scale.The Ti3Al+10at%Nb alloys used in this study were treated at 1060°C and then aged at 700°C for 2 hours. The specimens suitable for TEM were prepared by standard jet electrolytic-polishing technique. A JEM-200CX electron microscope with an interpretable resolution of about 0.25 nm was used for HREM.The [100] and [001] projections of the α2 phase were shown in Fig.l.The alloy obtained consist of at least two phases-α2(Ti3Al) and β0 structures. Moreover, a disorder α phase with small volume fraction was also observed. Fig.2 gives [100] and [001] diffraction patterns of the α2 phase. Since lattice parameters of the ordered α2 (a=0.579, c=0.466 nm) and disorder α phase (a0=0.294≈a/2, c0=0.468 nm) are almost the same, their diffraction patterns are difficult to be distinguished when they are overlapped with epitaxial orientation relationships.

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.

Observation of Hexagonal AiGaAs Grown by OMCVD

1990 ◽  
Vol 209 ◽  
Author(s):  
D. M. Hwang ◽  
T. S. Ravi ◽  
R. Bhat ◽  
S. Simhony ◽  
C. Y. Chen ◽  
...  
Keyword(s):  
High Resolution ◽  
Quantum Wire ◽  
Gaas Substrate ◽  
Hexagonal Phase ◽  
Stacking Faults ◽  
Hexagonal Structure ◽  
Cubic Phase ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Cladding Layers

ABSTRACTExtended regions of hexagonal zinc sulfide (wurtzite) structure are found to exist in AlGaAs grown by low-pressure OMCVD at 750°C. The specimen was prepared on a (001) GaAs substrate patterned with [110]-orientedV-grooves, intended for a quantum wire laser structure. A high density of planar faults was observed to originate in theAl0.66Ga0.34As cladding layers near the inner corners of the V-grooves and propagate towards the surface along the {111} planes. Many of these faults are stacking faults and microtwins. However, there also exhibit extended regions of hexagonal structure, revealed in electron diffraction patterns and high resolution lattice images. The hexagonal phase shares the same close-packed layers with the cubic phase, i.e., (0001)hexagonal // {111}cubic. The mechanism for the formation of hexagonal structure in this specimen is not yet fully understood.

Solid solution and cation ordering limits in high-temperature sodic pyroxenes from the Nybö eclogite pod, Norway

1981 ◽  
Vol 44 (333) ◽  
pp. 37-44 ◽  
Author(s):  
M. A. Carpenter ◽  
D. C. Smith
Keyword(s):  
High Temperatures ◽  
Short Range ◽  
Antiphase Domain ◽  
Stability Field ◽  
Cation Ordering ◽  
Two Phase ◽  
Selected Area Electron Diffraction ◽  
Short Range Ordering ◽  
Antiphase Domains ◽  
Diffraction Patterns

AbstractA range of sodic pyroxenes (Jd78Ac2Aug20Jd24Ac9Aug67) from the Nybö eclogite pod, Norway, have been examined by electron-microprobe analysis and by transmission electron microscopy.. Five different microprobes give generally compatible results and new analyses completely fill the natural composition gap in jadeite-rich omphacites with ∼ 3–12% acmite, confirming complete miscibility at high temperatures (⩾ 700 °C). Crystals with omphacite compositions around jadeite: augite = 1:1 contain antiphase domains resulting from the C2/c → P2/n cation ordering transformation. Exsolution microstructures were not observed, from which it is concluded that there are no two-phase regions separating the P2/n and C2/c stability fields at high temperatures (∼ 620–750 °C) and that cooling was too rapid for exsolution to occur in the jadeite/omphacite and omphacite/augite low-temperature solvi. Crystals whose compositions depart significantly from Jd:Aug= 1:1 have weak, diffuse h + k = odd reflections in selected area electron diffraction patterns which are interpreted as being due to short-range ordering outside the true P2/n stability field. The short-range ordering and lack of exsolution are consistent with a previous suggestion that the order/disorder transformation in omphacite is second (or higher) order in character. The average antiphase domain sizes (up to ∼ 3500 Å) are larger than any previously recorded in omphacites and are consistent with available petrological evidence for a long period of annealing at high temperatures before tectonic uplift and cooling.

A study of the ordered structures of the Au–Mn system by high-voltage–high-resolution electron microscopy. II. Two-dimensional antiphase structures based on the DO 22 structure

1981 ◽  
Vol 14 (6) ◽  
pp. 392-400 ◽  
Author(s):  
O. Terasaki ◽  
D. Watanabe ◽  
K. Hiraga ◽  
D. Shindo ◽  
M. Hirabayashi
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Antiphase Domain ◽  
Two Dimensional ◽  
Ordered Structures ◽  
Domain Structures ◽  
Resolution Electron ◽  
Specimen Area ◽  
High Resolution Structure ◽  
Resolution Structure

Two-dimensional antiphase domain structures existing in the composition range 20–23 at.% Mn were investigated by a high-resolution structure-imaging technique with a 1 MV electron microscope. The structures are based on the DO 22 structure and consist of parallelogram-shaped domains containing 4 × 3 columns of Mn atoms and lozenge-shaped domains with 4 × 4 and 3 × 3 columns, and the domains are separated by two-dimensional antiphase boundaries parallel to the ({\bar 2}40) and (240) planes of the fundamental face-centred structure. The configuration of the domains changes delicately with a slight change of composition or annealing temperature, and the symmetry of the structure is lowered below about 670 K. The ideal structure models have compositions of about 22.7 at.% Mn. The images of about half of the specimen area of the 22.6 at.% Mn alloy annealed at 570 K do not correspond to these new structures, but bear a resemblance to the image expected from the two-dimensional antiphase structure proposed by Watanabe [J. Phys. Soc. Jpn (1960), 15, 1030–1040] for Au3Mn, which is based on the L12 structure and has boundaries parallel to the (100) and (010) planes.

Ordering In Zn0.5Fe0.5Se Epilayers Grown on InP Substrates by Molecular Beam Epitaxy

1991 ◽  
Vol 231 ◽  
Author(s):  
L. Salamanca Riba ◽  
K. Park ◽  
B. T. Jonker
Keyword(s):  
High Resolution ◽  
Ordered Structure ◽  
Cross Sectional ◽  
Zinc Blende ◽  
Transmission Electron ◽  
Lattice Images ◽  
High Resolution Images ◽  
Diffraction Patterns ◽  
Inp Substrates ◽  
Image Simulations

AbstractWe have observed an ordered structure in Zn0.5Fe0.5Se epilayers grown on (001) InP substrates using transmission electron microscopy. The ordered structure of Zn0.5Fe0.5Se has Fe atoms occupying the (0,0,0) and (½, ½, 0) sites and Zn atoms occupying the (0, ½, ½) and (½, 0, ½) sites in the zinc-blende unit cell. Ordering is observed in both electron diffraction patterns and cross-sectional high-resolution lattice images along the < 100 > and < 110 > directions. This ordered structure consists of alternating ZnSe and FeSe monolayers along the < 100 > and < 110 > directions. Computer image simulations of the high-resolution images under various thicknesses, and defocusing conditions have been obtained and are compared with those obtained experimentally.

On Dark-Field High-Resolution Images Of Two-Dimensional Antiphase Structures

1983 ◽  
Vol 21 ◽  
Author(s):  
O. Terasaki ◽  
G.J. Wood ◽  
D. Watanabe
Keyword(s):  
High Resolution ◽  
Dark Field Image ◽  
Antiphase Domain ◽  
Dark Field ◽  
Two Dimensional ◽  
Domain Structures ◽  
Resolution Electron ◽  
True Representation ◽  
High Resolution Images ◽  
Electron Microscopes

ABSTRACTDark-field images of two-dimensional antiphase domain structures with stepped boundaries have been simulated for imaging conditions corresponding to some current high resolution electron microscopes. The simulations reveal that the positions of the dots in the dark-field images do not give a true representation of atomic structure; thus, in contrast to the brightfield superstructure images, it is very misleading to say that bright dots in the dark-field image correspond exactly to the positions of the minority atoms.

Atomic structural images of crystalline cholesterol monohydrate in human atheroma

1990 ◽  
Vol 48 (3) ◽  
pp. 206-207
Author(s):  
Ying-Shiung Lee
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Crystal Lattices ◽  
Resolution Electron ◽  
Lattice Images ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns ◽  
Cholesterol Monohydrate ◽  
Human Atheroma

To gain further insight regarding the micromechanisms of progression and regression of human atherosclerotic plaques the present study was designed for characterization of crystal lattices of cholesterol monohydrate, demonstration of cholesterol crystallization processes, and identification of crystal disorders of cholesterol monohydrate by means of high resolution electron microscopy (HREM).Clusters of cholesterol clefts containing crystalline cholesterol monohydrate were obtained from atherosclerotic human aortas under a dissecting microscope at autopsy. Cholesterol clefts were milled to a powder with a porcelain pestle. The powdered samples without staining dispersed in distilled water were spread on the copper-grid and dried at room temperature. The air-dried specimens were directly examined by a Hitachi H-9000 high resolution electron microscope operated at 300 KV. High resolution lattice images were taken under an optimal defocus condition. Selected area images and electron diffraction patterns were simultaneously taken for the analysis of crystalline characteristics.

Characterization of Dislocations and Interfaces in Semiconductors by High Resolution Electron Microscopy

1980 ◽  
Vol 2 ◽  
Author(s):  
J.C.H. Spence ◽  
A. Olsen
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Local Symmetry ◽  
Partial Dislocations ◽  
Resolution Electron ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
The Individual

ABSTRACTIt is not presently possible to resolve the individual atoms in any semiconductor by high resolution electron microscopy (HREM). However symmetry arguments may be used to allow near-atomic resolution lattice images to be interpreted in rare favorable cases. This method is applied to the problem of distinguishing shuffle and glide set partial dislocations in silicon. It is also proposed that two dimensional characteristic loss energy selected diffraction patterns be used to reveal the local symmetry about selected substitutional species implanted in semiconductor lattices.

Effects of illumination spot size on high-resolution image contrast for radiation-sensitive specimens

1986 ◽  
Vol 44 ◽  
pp. 14-17
Author(s):  
Kenneth H. Downing
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Spot Size ◽  
Image Contrast ◽  
Protein Crystals ◽  
Hexagonal Symmetry ◽  
High Resolution Image ◽  
Lattice Images ◽  
High Resolution Images ◽  
Diffraction Patterns

Electron diffraction patterns of a number of different protein crystals extend to well beyond 0.4 nm. However, until quite recently, no images of these crystals had been obtained which showed such high resolution. The recent introduction of monolayer crystals of paraffin, which diffract at 0.4 nm several thousand times as strongly as typical protein crystals, has made it possible to obtain such high-resolution images almost routinely, and has allowed the study of the causes for the previous lack of success. It has been found that the images of paraffin crystals fall far short of images which could be obtained under ideal circumstances. Not only do the images only rarely show the pseudo-hexagonal symmetry of the crystals, but quantitative analysis of lattice images has shown that under normal conditions the image contrast is typically only about 3-4% of that which is theoretically possible, based on the strength of electron diffraction spots.

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