Determine Crystal structure of non-cubic crystal in XRD plot

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Discussion Overview

The discussion focuses on determining the crystal structure of non-cubic crystals using X-ray diffraction (XRD) data, specifically analyzing 2theta and intensity values. Participants explore techniques for identifying lattice parameters a, b, and c, and the challenges associated with non-cubic structures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about methods to determine non-cubic crystal structures from XRD data, seeking resources or links for further information.
  • Another participant asks whether the analysis is intended as a manual exercise or through software, providing a link to a relevant resource.
  • A participant clarifies that the goal is to develop a program for determining non-cubic crystal structures and expresses difficulty in finding applicable patterns or techniques.
  • One proposed technique involves calculating Q^2 for observed reflections and matching them to assumed Miller indices, suggesting that this method works well for certain lattice types but is more complex for monoclinic and triclinic structures.
  • It is noted that systematic absences due to space groups may affect peak visibility, indicating that a thorough analysis must consider these factors when fitting data.

Areas of Agreement / Disagreement

Participants present various techniques and approaches without reaching a consensus on a singular method for determining non-cubic crystal structures. The discussion remains unresolved regarding the best practices for analysis.

Contextual Notes

Participants mention specific assumptions related to lattice angles and the potential impact of space groups on peak visibility, indicating that these factors may complicate the determination process.

Who May Find This Useful

This discussion may be useful for researchers and practitioners in materials science, crystallography, and related fields who are interested in XRD analysis of non-cubic crystals.

ralden
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Given only 2theta and intensity, how to know the crystal structure (except cubic) of non cubic crystals, and also determine their lattice parametera,b,and c, if there's a link or website discussing techniques to determine crystal structure of all crystals, please don't hesitate to put it here. thanks.
 
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Do you want to do this by hand as an exercise, or using software in a semi-production mode?

http://www.rigaku.com/downloads/journal/RJ26-2/RJ26-2_10-14.pdf
 
actually this is an exercise to make a program that can determine the crystal structure of non-cubic, I'm having a problem in finding a pattern or techniques to determine non-crystal structure unlike cubic.
 
One technique seems to be to calculate Q^2 for all observed reflections, then assume the lowest reflections are (100), (110), (111), (200), ... and see what matches.

If your lattice angles are all 90 deg, then Q^2 = H^2 a*^2 + K^2 b*^2 + L^2 c*^2. For hexagonal this also seems to work quite well. For monoclinic and triclinic this is more of a mess.

I guess in a computer programme one could one by one go through the 14 Bravais lattices, add a few assumptions to each one (like a>c or a<c for tetragonal, as this could invert the order of peaks), and calculate the lattice parameters from the first few reflections.

Note that the space group may lead to systematic absence of certain peaks, so a better critirium for fit/no fit is if there are peaks in the data that have no corresponding HKL.
 

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