Weak Spots Related to Superstructures in Electron Diffractions
- Practical Electron Microscopy and Database -
- An Online Book -

http://www.globalsino.com/EM/  



 
This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

=================================================================================

Superstructures can appear in company with disordering or less-ordering of some atomic arrangements. For instance, two niobium tungsten oxides (Nb7W10O47.5 and Nb4W13O49) consist often of less-ordered arrangements of filled tunnels, causing the diffuse scattering in electron diffraction. Figure 2327a shows the electron diffraction patterns (along [001]) of two crystallites of Nb7W10O47.5 presenting circular diffuse scattering in different degrees, which appears around the main bright reflections of the basic TTB substructure. In Nb4W13O49 as shown in Figure 2327b, the diffuse scattering pattern is cross-shaped due to the presence of long slabs of diamond-linked pentagonal columns. Overall, the origin of the diffuse scatterings is presumably the presence of short-range order in the PC (pentagonal columns) sublattice [1], or an intermediate state of order (or called transition state [2]) between a random arrangement and a long-range ordered structure. In addition, the weak spots indicate TTB superstructures.

The electron diffraction patterns (along [001]) of two crystallites of Nb7W10O47.5

Figure 2327a. The electron diffraction patterns (along [001]) of two crystallites of Nb7W10O47.5. Adapted from [3]

The electron diffraction patterns (along [001]) of two crystallites of Nb4W13O49

Figure 2327b. The electron diffraction patterns (along [001]) of a Nb4W13O49 crystallite. Adapted from [3]

Figure 2327c shows the [100] electron diffraction pattern and intensity distribution in the reciprocal lattice of TiN0.61.

[100] electron diffraction pattern and intensity distribution in the reciprocal lattice of TiN0.61

Figure 2327c. The [100] electron diffraction pattern and intensity distribution in the reciprocal lattice of TiN0.61. The large circles in (b) show the fundamental reflexions, while the small circles in (b) show the superstructure reflexions. Adapted from [4]

 

 

 

 

 

 



 

 

 

 

 

 

 

 

[1] Iijima, S. & Cowley, J. M. (1977). J. Phys. Colloq. 38, 135-144.
[2] Amelinckx, S. (1992). Materials Science and Technology, Vol. 2A, Characterisation of Materials, Part. I, pp. 1-146. Weinheim: Verlag Chemie.
[3] Frank Krumeich, Order and Disorder in Niobium Tungsten Oxides of the Tetragonal Tungsten Bronze Type, Acta Cryst. (1998). B54, 240-249.
[4] S. Nagakura and T. Kusunoki, Journal of Applied Crystallography 10 (1977) 52.

 

 

=================================================================================

The book author (Dr Y. Liao) welcomes your comments, suggestions, and corrections, please click here for submission. You can click How to Cite This Book to cite this book. If you let Dr Y. Liao know once you have cited this book, the brief information of your publication will appear on the “Times Cited” page.



 
 
 
Copyright (C) 2006 GlobalSino, All Rights Reserved