Experimental determination of low order structure factors in the intermetallic compound TiAl

1993 ◽  
Vol 170 (1-2) ◽  
pp. 227-235 ◽  
Author(s):  
S. Swaminathan ◽  
I.P. Jones ◽  
N.J. Zaluzec ◽  
D.M. Maher ◽  
H.L. Fraser
Keyword(s):  
Intermetallic Compound ◽  
Experimental Determination ◽  
Order Structure ◽  
Structure Factors ◽  
Compound Tial ◽  
Low Order

scholarly journals Simple Method for Estimating the Contribution of Neighbouring n-beam Interactions to Two-beam Structure Factors

1988 ◽  
Vol 41 (3) ◽  
pp. 469
Author(s):  
HJ Juretschke ◽  
HK Wagenfeld
Keyword(s):  
Experimental Determination ◽  
Structure Factor ◽  
Beam Structure ◽  
Simple Method ◽  
Experimental Configuration ◽  
Structure Factors ◽  
Special Cases ◽  
Better Than

Unless special precautions are taken, the experimental determination of two-beam structure factors to better than 1 % may include contributions from neighbouring n-beam interactions. In any particular experimental configuration, corrections for such contributions are easily carried out using the modified two-beam structure factor formalism developed recently (Juretschke 1984), once the full indexing of the pertinent n-beam interactions is known. The method is illustrated for both weak and strong primary reflections and its applicability in special cases, as well as for less than perfect crystals, is discussed.

scholarly journals On the experimental determination of low-order structure factors in TiAl by energy-filtered convergent-beam electron diffraction

1993 ◽  
Vol 51 ◽  
pp. 662-663
Author(s):  
S. Swaminathan ◽  
I. P. Jones ◽  
N. J. Zaluzec ◽  
D. M. Maher ◽  
H. L. Fraser
Keyword(s):  
Electron Diffraction ◽  
Charge Density ◽  
Structure Factor ◽  
Convergent Beam Electron Diffraction ◽  
Order Structure ◽  
Electron Charge Density ◽  
Beam Electron ◽  
Structure Factors ◽  
Convergent Beam ◽  
Low Order

It has been claimed that the effective Peierls stresses and mobilities of certain dislocations in TiAl are influenced by the anisotropy of bonding charge densities. This claim is based on the angular variation of electron charge density calculated by theory. It is important to verify the results of these calculations experimentally, and the present paper describes a series of such experiments. A description of the bonding charge density distribution in materials can be obtained by utilizing the charge deformation density (Δρ (r)) defined by(1) where V is the volume of the unit cell, Fobs is the experimentally determined low order structure factor and Fcalc is the structure factor calculated using the Hartree-Fock neutral atom model. To determine the experimental low order structure factors, a technique involving a combination of convergent beam electron diffraction (CBED) and electron energy loss spectroscopy (EELS) has been used.

Quantitative Convergent Beam Electron Diffraction Measurements of Low-Order Structure Factors in Copper

2003 ◽  
Vol 9 (5) ◽  
pp. 379-389 ◽  
Author(s):  
Jesper Friis ◽  
Bin Jiang ◽  
John C.H. Spence ◽  
Randi Holmestad
Keyword(s):  
Electron Diffraction ◽  
High Energy ◽  
Convergent Beam Electron Diffraction ◽  
Order Structure ◽  
Band Theory ◽  
Beam Electron ◽  
Structure Factors ◽  
A Charge ◽  
Convergent Beam ◽  
Low Order

Accurate low-order structure factors for copper metal have been measured by quantitative convergent beam electron diffraction (QCBED). The standard deviation of the measured structure factors is equal to or smaller than the most accurate measurement by any other method, including X-ray single crystal Pendellösung, Bragg γ-ray diffraction, and high-energy electron diffraction. The electron structure factor for the (440) reflection was used to determine the Debye-Waller (DW) factor. The local heating of the specimen by the electron beam is determined to be 5 K under the current illumination conditions. The low-order structure factors for copper measured by different methods are compared and discussed. The new data set is used to test band theory and to obtain a charge density map. The charge deformation map shows a charge surplus between the atoms and agrees fairly well with the simple model of copper 2+ ions at the atomic sites in a sea of free uniformly distributed electrons.

Measurement of low-order structure factors for silicon from zone-axis CBED patterns

1995 ◽  
Vol 60 (2) ◽  
pp. 311-323 ◽  
Author(s):  
M Saunders ◽  
D.M Bird ◽  
N.J Zaluzec ◽  
W.G Burgess ◽  
A.R Preston ◽  
...  
Keyword(s):  
Zone Axis ◽  
Order Structure ◽  
Structure Factors ◽  
Low Order

On the accuracy of structure-factor measurements in GaAs by CBED

1988 ◽  
Vol 46 ◽  
pp. 824-825
Author(s):  
J.M. Zuo ◽  
M. O'Keeffe ◽  
J.C.H. Spence
Keyword(s):  
Structure Factor ◽  
Phonon Scattering ◽  
Three Dimensional ◽  
Bloch Wave ◽  
Bragg Angle ◽  
Order Structure ◽  
Structure Factors ◽  
Convergent Beam ◽  
Electron Energy Loss ◽  
Low Order

By comparing the experimental intensity in convergent-beam electron diffraction (CBED) patterns along the [h,0,0], [h,h,0] and [h,h,h] systematics directions with three-dimensional Bloch-wave calculations, we have refined the low-order structure factor amplitudes of GaAs. (For Si, see) The experimental data were collected using a Philips EM400 electron microscope and a Gatan model 607 electron energy loss spectrometer (EELS) tuned to the elastic peak. By placing the scan coils of the microscope under the control of a PDP11 computer, the CBED patterns could be scanned over the EELS entrance slit. Data were collected at 120kV and -183°C to reduce phonon scattering and contamination. The angular resolution was 0.6% of the (200) Bragg angle. The refinement parameters in the calculations were high voltage (obtained from HOLZ lines), thickness (obtained from outer CBED fringes), absorption potentials (from the asymmetry of the (000) disk) and the low-order structure factors Vg (from inner peaks).

Quantitative Convergent Beam Electron Diffraction (CBED) Measurements of Low-Order Structure Factors in Nickel

1997 ◽  
Vol 3 (S2) ◽  
pp. 1013-1014
Author(s):  
M. Saunders ◽  
A. G. Fox ◽  
P. A. Midgley
Keyword(s):  
Experimental Studies ◽  
Zone Axis ◽  
Order Structure ◽  
Data Set ◽  
Crystalline Materials ◽  
Charge Densities ◽  
Structure Factors ◽  
Convergent Beam ◽  
Best Fit ◽  
Low Order

The introduction of quantitative CBED techniques in recent years has led to experimental studies of charge densities in crystalline materials with unprecedented accuracy. Despite these successes, the development process is still on-going with the aim of gaining a better understanding of the techniques. With this in mind, we have undertaken a systematic study of the low-order structure factors of nickel using the ZAPMATCH zone-axis pattern matching technique of Bird and Saunders. In this approach, a set of low-order structure factors (both elastic and absorptive components) is adjusted until a best-fit is obtained between a many-beam simulation and an elastic filtered zone-axis pattern. Additional higher-order structure factors are included to converge the scattering potential but are kept fixed at neutral atom values during the fit. The questions we set out to address are (i) how to choose the correct number of structure factors to refine from a given data-set, (ii) are the absorptive structure factor components we refine of any use, and (iii) can we determine Debye-Waller factors at the same time as we measure the charge density? The first two points are discussed here.

Sign in / Sign up

Export Citation Format

Share Document