Using SAED we would have some bright points reflecting the orientation of a specific phase?
Would you please let me know how I can analyze them and get to know the related phase?
Thank you!
Dear Ahmad,
A brief background : Each spot on the SAED pattern corresponds to an {hkl} value. (If the grains are very fine, the spots may merge to form rings). The 'indexing' process is essentially determining these {hkl} values. Once you know each of the {hkl} values, the geometric/angular relationships between the different planes can be found. This tells (a)what the crystal structure is (phase) and (b) how it is oriented.
Now, coming to the theory of indexing. The SAED pattern will have a central spot, which indicates the crystallographic direction parallel to the electron beam (this is the orientation information'). The distance(say 'r') from the central spot to any spot is inversely proportional to the d-spacing ('d' in Bragg's law) of the corresponding {hkl} plane. As in XRD, the d values of different planes have characteristic ratios dependent on the crystal structure (dependent on the angle between the planes, again using Bragg's law).
I hope that gives some background. For step-by-step practical procedure, please see this nice discussion with many useful tutorial links:
https://www.researchgate.net/post/How_do_we_calculate_d-spaces_from_SAED_pattern/1
Additionally, for more complicated microstructures including twins, multiple phases etc, the book 'A Practical Guide to Transmission Electron Microscopy- Fundamentals' by Zhiping Luo can be a nice place to start. (There may be resources better suited to you, this is just one book that I found useful).
Good luck!
.
Diameter of the SAED image bright spots are almost equal to the d spacing for a particular hkl value plane. 1st find the d spacing for your hkl value and then compare with diameter of the spot.
Dear Ahmad,
A brief background : Each spot on the SAED pattern corresponds to an {hkl} value. (If the grains are very fine, the spots may merge to form rings). The 'indexing' process is essentially determining these {hkl} values. Once you know each of the {hkl} values, the geometric/angular relationships between the different planes can be found. This tells (a)what the crystal structure is (phase) and (b) how it is oriented.
Now, coming to the theory of indexing. The SAED pattern will have a central spot, which indicates the crystallographic direction parallel to the electron beam (this is the orientation information'). The distance(say 'r') from the central spot to any spot is inversely proportional to the d-spacing ('d' in Bragg's law) of the corresponding {hkl} plane. As in XRD, the d values of different planes have characteristic ratios dependent on the crystal structure (dependent on the angle between the planes, again using Bragg's law).
I hope that gives some background. For step-by-step practical procedure, please see this nice discussion with many useful tutorial links:
https://www.researchgate.net/post/How_do_we_calculate_d-spaces_from_SAED_pattern/1
Additionally, for more complicated microstructures including twins, multiple phases etc, the book 'A Practical Guide to Transmission Electron Microscopy- Fundamentals' by Zhiping Luo can be a nice place to start. (There may be resources better suited to you, this is just one book that I found useful).
Good luck!
.
I agree with Aashranth. The phase structure of the crystal obtained from SAED might be confirmed by indexing with hkl values of XRD. To be sure about the crystal structure, XRD analysis is mandatory.
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