How to index single crystal Bragg peaks

In summary, the conversation discusses using XRD and XRF techniques to index Bragg peaks for powder diffraction and single cubic crystals of NaCl. The speaker has encountered difficulties in obtaining expected sequences of allowed reflections for cubic lattices and determining hkl values from the angle of diffraction. They also inquire about the possibility of using standard techniques for powder sample calculations on a single crystal. The response suggests experimenting with different orientations and rotating the crystal to achieve a 2D pattern. Tumbling on two axes may also be necessary to achieve a powder-like appearance.
  • #1
Hello890
12
0
I am able to find methods on how to index Bragg peaks for powder diffraction, and was wondering if the method is the same for single cubic crystals of NaCl? I have tried and cannot get the expected sequence of allowed reflections for cubic lattices (h^2 + k^2 + l^2= 3, 4, 8, 11, 12, 16, 19, ...). Instead I am getting the sequence as 3, 13, 32.

The experiment was done simply by observing the XRD pattern from a single cubic crystal of NaCl, collected using Cu kalpha (wavelength = 154pm).

Also, how do I determine the hkl values from the angle of diffraction? ie: which planes will lead to constructive interference?
 
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  • #2
Powder will give you many orientations so all possible internal reflections will appear.
Depending on it's orientation, a single crystal will provide a greatly restricted number of peaks.

XRD a single crystal, then crush it to powder and repeat the XRD. Is there a difference?
 
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  • #3
Baluncore said:
Powder will give you many orientations so all possible internal reflections will appear.
Depending on it's orientation, a single crystal will provide a greatly restricted number of peaks.

XRF a single crystal, then crush it to powder and repeat the XRF. Is there a difference?
Many thanks for your reply. Unfortunately I am not allowed to powder the sample. Also, could I use standard techniques for powder sample calcuations to calculate the relative intensities of the peaks for this single crystal?
 
  • #4
I would suggest that you experiment; obtain another salt crystal from the kitchen, then obtain data from that oriented crystal before crushing it to powder and repeating the process.

I do not know the make and model of your X-Ray diffractometer, or how it is arranged. If you rotate the single cubic crystal while it is axially aligned with the rotation, then the pattern will be of a 2D, not a 3D structure. Many spacing combinations may be missing.

To make a single crystal look like a powder you would need to tumble it on two axes. Depending on the instrument, that may be possible.
 

FAQ: How to index single crystal Bragg peaks

What is the process of indexing single crystal Bragg peaks?

Indexing single crystal Bragg peaks is the process of determining the orientation and the lattice parameters of a crystal from the positions of its diffraction peaks. It involves measuring the angles and intensities of the Bragg peaks and comparing them to known reference values to identify the crystal lattice and its orientation in space.

What are the necessary equipment for indexing single crystal Bragg peaks?

The necessary equipment for indexing single crystal Bragg peaks include a diffractometer, a source of monochromatic X-rays, a sample holder, and a detector. These instruments are used to measure the angles and intensities of the Bragg peaks, which are essential for indexing.

What are the main challenges in indexing single crystal Bragg peaks?

The main challenges in indexing single crystal Bragg peaks include identifying the correct crystal lattice and orientation from a large number of potential solutions, dealing with overlapping or weak peaks, and handling systematic errors in the measurement data. These challenges require careful data analysis and thorough understanding of crystallographic principles.

Can software be used for indexing single crystal Bragg peaks?

Yes, software can be used for indexing single crystal Bragg peaks. There are various software packages available that can assist with data analysis and indexing, such as CrysAlisPro, XDS, and Denzo. However, it is important to have a good understanding of the underlying principles and to verify the results obtained from the software.

What are the applications of indexing single crystal Bragg peaks in scientific research?

Indexing single crystal Bragg peaks has various applications in scientific research, such as determining the crystal structure of new materials, studying the orientation and texture of crystalline materials, and investigating the effects of defects and imperfections on crystal properties. It is also used in fields such as materials science, geology, and biology to understand the structure and behavior of crystalline materials.

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