Position of Incommensurate Satellites Appearing in Ti-Ni Based Shape Memory Alloys

2011 ◽  
Vol 172-174 ◽  
pp. 150-154
Author(s):  
Mitsuharu Todai ◽  
Takashi Fukuda ◽  
Tomoyuki Kakeshita
Keyword(s):  
Electron Diffraction ◽  
Temperature Dependence ◽  
Negative Temperature ◽  
Zone Axis ◽  
The Other ◽  
Phonon Softening ◽  
Modulated Structure ◽  
Propagation Vector ◽  
Displacement Direction ◽  
Diffraction Patterns

We have investigated electron diffraction patterns of a Ti-44Ni-6Fe alloy exhibitng a negative temperature dependence in electrical resistivity below Tmin = 210 K. The electron diffraction patterns taken near Tmin show diffuse satellites at gB2 + <zζ0>* when the zone axis is [111] and [001]. For both the beam directions, the value ζ is slightly smaller than 1/3. On the other hand, the satellites are missing when the zone axis is [110]. This means that the incommensurate phase has a modulated structure with the propagation vector <zζ0>* (ζ~1/3) and the displacement direction is one of <110> which is vertical to the propagation vector. This modulation is obviously the consequence of the phonon softening of TA2-branch with the propagation vector near <zζ0>* (ζ~1/3). In addition to the satellite at gB2 + <zζ0>* (ζ~1/3), satellites appear at gB2+<zζ0>* with ζ = 1/2 when the zone axis is [001] and rod-like steaks appear in <112>* direction when the zone axis is [110]. However, these satellites and rod-like streaks do not show clear temperature dependence, suggesting they are not directly related to the phonon softening of TA2-branch.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

A study of the high-Cu Al–Cu–Co decagonal phase

1993 ◽  
Vol 8 (7) ◽  
pp. 1473-1476 ◽  
Author(s):  
B. Grushko
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Electron Diffraction ◽  
Diffuse Scattering ◽  
Nonequilibrium State ◽  
Zone Axis ◽  
Decagonal Phase ◽  
Diffraction Patterns ◽  
Scanning Electron

The decagonal phase was studied by transmission and scanning electron microscopy in an Al62Cu24Co14 alloy annealed at 550–850 °C. The electron diffraction patterns of the decagonal phase exhibited weak quasiperiodic odd-n reflections in the [1-2100] zone axis corresponding to the equilibrated structure. The relative intensities of these reflections were significantly lower in the Al62Cu24Co14 than in the Al68Cu11Co21 decagonal phase. Diffuse scattering observed previously at the same positions can be related to a nonequilibrium state of the decagonal phase.

Enantiomorph identification of crystals belonging to the point groups 321 and 312 by convergent-beam electron diffraction

2007 ◽  
Vol 40 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Haruyuki Inui ◽  
Akihiro Fujii ◽  
Hiroki Sakamoto ◽  
Satoshi Fujio ◽  
Katsushi Tanaka
Keyword(s):  
Electron Diffraction ◽  
Diffraction Method ◽  
Convergent Beam Electron Diffraction ◽  
Zone Axis ◽  
The Other ◽  
Zeroth Order ◽  
Beam Electron ◽  
First Order ◽  
Point Groups ◽  
Convergent Beam

The recently proposed CBED (convergent-beam electron diffraction) method for enantiomorph identification has been successfully applied to crystals belonging to the point groups 321 and 312. The intensity asymmetry of zeroth-order Laue zone and/or first-order Laue zone reflections of Bijvoet pairs is easily recognized in CBED patterns with the incidence along appropriate zone-axis orientations for each member of the enantiomorphic pair. The intensity asymmetry with respect to the symmetry line is reversed upon changing the space group (handedness) from one to the other. Thus, enantiomorph identification can be easily performed in principle for all crystals belonging to the point groups 321 and 312.

Energy Filtered Imaging and Convergent Beam Electron Diffraction (CBED) in the Transmission Electron Microscope (TEM)

1997 ◽  
Vol 3 (S2) ◽  
pp. 973-974
Author(s):  
A.G. Fox ◽  
E.S.K. Menon ◽  
M. Saunders
Keyword(s):  
Electron Diffraction ◽  
Form Factors ◽  
Zone Axis ◽  
X Ray ◽  
Elemental Imaging ◽  
Energy Filtering ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Convergent Beam ◽  
Single Objective

Over the last ten years TEMs have been developed that are capable of HREM, EDX, PEELS and diffraction using a single objective pole piece. More recently these TEMs have been equipped with the capability of energy filtering the electron beam after it has passed through the sample so that energy filtered images and electron diffraction patterns can be obtained. In this work the use of a Topcon 002B TEM equipped with a GATAN PEELS imaging filter (GIF) to generate zero-loss energy filtered zone axis CBED patterns and elemental images from inelastically scattered electrons will be described. An analysis of this energy filtered data indicates that elemental imaging using the GIF is an informative, but semiquantitative technique, whereas zero-loss energy filtered zone axis CBED patterns can be accurately quantified so that the two lowest-angle x-ray form factors of cubic elements can be measured with errors of the order of 0.1% or less.

[001] imaging of rutile: A problem in high-resolution microscopy

1983 ◽  
Vol 41 ◽  
pp. 292-293
Author(s):  
Peter G. Self ◽  
Peter R. Buseck
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Computer Simulations ◽  
Zone Axis ◽  
Severe Problem ◽  
Diffraction Patterns ◽  
High Resolution Microscopy

HRTEM images of the [001] zone of rutile (fig. 1) show 0.32 nm fringes near the edge of the crystal, but these rapidly change to 0.46 nm in the thicker parts of the crystal. This change in spacing is only possible if the intensities in the dynamically forbidden {100} reflections become comparable to the intensities of the {110} reflections. The {100} reflections are dynamically forbidden because the structure has 2-fold screw axes parallel to a and b and n-glides perpendicular to a and b. The presence of 0.46 nm rather than 0.32 nm fringe spacings in images of the thicker crystal regions presents a severe problem in matching the images to computer simulations. Fig. 2 shows [001] zone axis images for thin and thick crystals. As expected from symmetry, the computed images show only 0.32 nm spacings. In an attempt to explain the mismatch between computed and experimental images several effects not normally included in image calculations, and which could cause a change in the symmetry of electron diffraction patterns, were investigated, all without success.

The Determination of Rotation Axis in the Rotation Electron Diffraction Technique

2013 ◽  
Vol 19 (5) ◽  
pp. 1276-1280 ◽  
Author(s):  
Mika Buxhuku ◽  
Vidar Hansen ◽  
Peter Oleynikov ◽  
Jon Gjønnes
Keyword(s):  
Electron Diffraction ◽  
Rotation Axis ◽  
Incident Beam ◽  
Zone Axis ◽  
Crystallographic Direction ◽  
Accurate Knowledge ◽  
Electron Diffraction Technique ◽  
Diffraction Patterns

AbstractMethods to determine the rotation axis using the rotation electron diffraction technique are described. A combination of rotation axis tilt, beam tilt, and simulated experimental diffraction patterns with nonintegers zone axis has been used. Accurate knowledge of the crystallographic direction of the incident beam for deducing the excitation error of reflections simultaneously near Bragg positions is essential in quantitative electron diffraction. Experimental patterns from CoP3 are used as examples.

Tem Observance and Analysis of the (000l), l=2n+l, Forbidden Reflections in Synthetic and Biological Hydroxyapatites

1999 ◽  
Vol 599 ◽  
Author(s):  
J. Reyes-Gasga ◽  
M. Reyes-Reyes ◽  
R. García-García
Keyword(s):  
Electron Diffraction ◽  
Tooth Enamel ◽  
Structural Disorder ◽  
Human Tooth ◽  
Double Diffraction ◽  
Modulated Structure ◽  
Human Tooth Enamel ◽  
Modulated Structures ◽  
Diffraction Patterns

AbstractThe systematic appearance of (000l), l=2n+1, forbidden reflections in the electron diffraction patterns of hydroxyapatite, both synthetic and natural (human tooth enamel), is discussed. Structural disorder, double diffraction, and modulated structures and are discussed as possible causes. Structural disorder and modulated structure could be responsible for the rupture of the reported symmetry, in which oxygen and hydrogen perform an important role.

Electron diffraction from anthracene

1996 ◽  
Vol 54 ◽  
pp. 688-689
Author(s):  
W. F. Tivol ◽  
J. H. Kim
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Room Temperature ◽  
Three Dimensional ◽  
Zone Axis ◽  
Data Set ◽  
High Resolution Data ◽  
Diffraction Patterns ◽  
Reduced Temperature ◽  
Resolution Data

Collection of a three-dimensional data set from anthracene illustrates some of the difficulties which can be encountered. Since the crystals are grown from solution their orientation is not certain, and the crystals are very bendy, so a range of orientations is encountered at a given tilt setting. Anthracene is moderately labile to irradiation, so care must be taken to avoid radiation damage during data collection. Anthracene will sublime at room temperature under vacuum, so the data must be collected at reduced temperature. Flat, well-ordered areas of the crystals are rare, so collection of high-resolution data is time-consuming. The thickness of the crystals is difficult to control, so finding areas which have minimal multiple scattering is also formidable.The structure of anthracene is already known, so simulations of the diffraction patterns along various zone axes can be made. Cerius 2.0® was used to produce simulated zone axis patterns for all combinations of indices whose absolute values were 3 or less. The preferred orientation for the untilted grid is [102]. Scans of several preparations resulted in patterns which matched the simulation for [102]. The angles for each of the Miller planes with respect to [102] were calculated from the formula given by Dorset.

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