I have SAD analyses, d-spacing list, but no Miller indices. When I looked up in PDF4 possible minerals that I suspect in a sample, they all match. They all have similar d-spacing, like (rounded) 1.9, 1.7, 1.3, and 1.1. How do I clarify or calculate Miller indices? Are degrees to spot data helpful?
It seems to be easy, finally it is easy, but if you have to do it you need to combine a few simple crystallographic laws and equations.
The respective equations are well known but unfortunately not all published together at the same place. Therefore, I submitted a paper which is already available at Researchgate:
Article A little geometric crystallography for EBSD and related techniques
SAED is a related technique :-).
Still a final remark: Many things appear to be easy, but the more you know about it the more you realize that this entire problem is more complicated than expected. The interpretation of SAED needs a bit experience. One image only displays a certain (incomplete) reciprocal lattice plane. If you know the plane you can index the spots. If you do not know anything you can index but your hkl won't match the hkl other people use, and a search in a database dos not make much sense. The major task is to find the basis vectors...and with a single pattern you cannot do it. You can define some but this is not sufficient.
Oh dear! If you want advice you need to be more specific about your minerals you have and equipment you use (for example your TEM should be equipped with EDS system and probably is!). Use this EDS to get chemistry of your grains and match it with respective diffraction patterns. Both d-values as well as angles are here critical to find Miller Indices. Remember our measurements of angles are far more accurate than measurement of d-values.
Go to book :
Andrews, K.W., Dyson, D.J., Keown, S.R. (1967) Interpretation of electron diffraction patterns. Helger & Watts, London, 188pp.
Electron diffraction patterns are characteristic to mineral systems and orientation of the beam to crystallographic orientation. The book gives basic examples how basic orientations in different crystallographic systems are looking like, but an exact identification requires measurement of d-values and angles and needs to be compared with calculated d-values and angles. All equations are in the book. Good luck. Harry Kucha
Thank you, Gert Nolze and Harry Kucha!
I oxidized zero valent iron and I know there should be ferrihydrite or goethite or magnetite or most likely a mixture. (I don’t need EDS in this case) But from library, they all have very similar d-spacing, that’s why it’s tricky. Ill check out the book, and the paper. Thanks!
Hi Daria,
some phases are really very different to distinguish by electrons. My recommendations are:
1.) try to get spot diffraction pattern from every phase,
2.) from every phase you have to acquire two or more zone-axis pattern. There are phases which may have the same patterns in few specific zone-axis,
3.) use as small camera lenght as is available on your TEM, to imagine FOLZ reflections. Two phases, which appear the same in ZOLZ patterns, are usually different in FOLZs.
Best of luck!
- Badges
- Science topic
- Similar topics
- Automotive Engineering
- Machines