Determination of six new polytypes in parisite-(Ce) by means of high resolution electron microscopy

2001 ◽  
Vol 65 (6) ◽  
pp. 797-806 ◽  
Author(s):  
Meng Dawei ◽  
Wu Xiuling ◽  
Mou Tao ◽  
Li Douxing
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Mineral Deposit ◽  
Space Groups ◽  
Selected Area Electron Diffraction ◽  
Resolution Electron ◽  
Rare Earth Mineral ◽  
Probable Space

AbstractThe ultrastructures of parisite-(Ce) from a rare-earth mineral deposit of Sichuan Province, southwest China, have been observed and investigated by selected area electron diffraction (SAED) and high resolution electron microscopy (HREM). Six new polytypes 4H, 10H, 16H, 18R, 24R and 30R were determined in parisite-(Ce), as were their crystal structure types, subcell (a′c‴, a′c″, a′c′) and supercell (ac) parameters, reflection conditions, polytype features and probable space groups. The HREM studies revealed the complex polytypism in parisite-(Ce) whereby the six new polytypes, formed by long-period ordered stacking, always coexist with the common polytype parisite-(Ce)-6R by syntaxy and thus constitute the complex microstructural ‘syntactic polycrystals’, the host of which is the polytype parisite-(Ce)-6R.

Orientation Relationship between Fe2M and Martensite in M50NiL Steel

2013 ◽  
Vol 456 ◽  
pp. 533-536
Author(s):  
Yan Zhi Lou
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Orientation Relationship ◽  
High Resolution Electron Microscopy ◽  
Lattice Parameters ◽  
Selected Area Electron Diffraction ◽  
Resolution Electron ◽  
Martensite Matrix

In this paper, high resolution electron microscopy (HREM) was used to observe nanosized Fe2M precipitates in M50NiL steel, and crystal structure of which was also investigated by selected area electron diffraction (SAED). At the same time, the orientation relationship between the Fe2M and the martensite matrix was also studied. The results suggested that crystal structure of Fe2M is close-packed hexagonal, and lattice parameters about a=b=0.473nm, c=0.772nm, α=β=90°, γ=120°. The orientation relationship between the nanoprecipitates Fe2M and martensite is and .

Microstructural determination of a metastable phase during rhodium oxidation

1989 ◽  
Vol 47 ◽  
pp. 262-263
Author(s):  
A. David Logan
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Volume Expansion ◽  
Lattice Structure ◽  
Metastable Phase ◽  
Active Surface ◽  
High Resolution Electron Microscopy ◽  
Silica Spheres ◽  
Resolution Electron

In heterogeneous catalysis, oxidation of the catalyst is frequently used as a means of removing impurities from the active surface. However, bulk oxidation severely alters the microstructure of the metal due to atom repositioning and valence changes. Transformation of Rh to Rh2O3 causes the lattice structure to change from fcc to hexagonal with a resulting volume expansion of 90% due to density changes. This is the reported cause for fracturing of crystallites and variations in reactivity. In this study, microstructural changes during progressive oxidation of 5 nm metal Rh particles have been examined.A 2 wt% Rh/Silica catalyst was prepared using Rh(III)-2,4 pentanedionate as a precursor and nonporous silica spheres as a support. The catalyst was then reduced in flowing H2 at 473 K. High resolution electron microscopy (HREM) was performed on a JEM-4000EX having a point resolution of 0.17 nm. The catalyst was oxidized in research purity O2 (Matheson 99.99%) using an all glass volumetric chemisorption system.

Image Deconvolution - An Effective Tool of Crystal Structure and Defect Determination in High-Resolution Electron Microscopy

2009 ◽  
Vol 1184 ◽  
Author(s):  
Fanghua Li ◽  
Chunyan Tang
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Image Deconvolution ◽  
One Dimensional ◽  
Modulated Structures ◽  
Resolution Electron ◽  
Different Types

AbstractImage deconvolution is introduced as an effective tool to enhance the determination of crystal structures and defects in high-resolution electron microscopy. The essence is to transform a single image that does not intuitively represent the examined crystal structure into the structure image. The principle and method of image deconvolution together with the related image contrast theory, the pseudo weak phase object approximation (pseudo WPOA), are briefly described. The method has been applied to different types of dislocations, twin boundaries, stacking faults, and one-dimensional incommensurate modulated structures. Results on the semiconducting epilayers Si0.76Ge0.24/Si and 3C-SiC/Si are given in some detail. The results on other compounds including AlSb/GaAs, GaN, Y0.6Na0.4Ba2Cu2.7Zn0.3O7-δ, Ca0.28Ba0.72Nb2O6 and Bi2.31Sr1.69CuO6+δ are briefly summarized. It is also shown how to recognize atoms of Si from C based on the pseudo WPOA, when the defect structures in SiC was determined at the atomic level with a 200 kV LaB6 microscope.

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