Unexpected Peaks in XRD: Causes Besides Doping?

  • Thread starter drizzle
  • Start date
In summary, when an unexpected peak appears in an XRD pattern of a pure material, it could be due to various factors such as superlattices, different lattice structures, vacancies, defects, or impurities from incomplete reaction. The peak height does not necessarily indicate the mass fraction of the compound, as the scattering power of different compounds may differ.
  • #1
drizzle
Gold Member
200
57
what possible explanation to an unexpected peak that may appear in an XRD pattern of a pure material [not doped, as far as I know the extra peaks that may occur would be due to the dopants], what causes, other than doping, could show alien peaks in a pure compound? thanks in advance
 
Physics news on Phys.org
  • #2
drizzle said:
what possible explanation to an unexpected peak that may appear in an XRD pattern of a pure material [not doped, as far as I know the extra peaks that may occur would be due to the dopants], what causes, other than doping, could show alien peaks in a pure compound? thanks in advance

You need to explain what you mean by a "pure material". Is this a single-crystal throughout, or do you just require that it is made up of only one type of material that you say, is undoped?

If the material has something called a "superlattice", then that will show up as an extra peak. If it is made up of only one type of atoms, but it can have two or more different lattice structures, that that will show up as additional peaks. Vacancies and defects will also do the same. Etc... etc.

Zz.
 
  • #3
thanks for replying ZapperZ, it's a metal oxide compound [in a powder form], this material has a number of knowable peaks each at a certain (hkl) plane [recorded in JPDS cards], however, a number of extra peaks show in the XRD pattern [none of them matches with the known peaks of this material], I thought of defects as a possible candidate, but it doesn’t sound reasonable, cause those peaks aren’t small ones [a number of them have high intensities], I could be wrong though...is the synthesis method of this material a possible cause to those peaks? [I mean to form defects in the material which in turn lead to those peaks]
 
Last edited:
  • #4
If your starting materials used to create your compound didn't react completely, you will see peaks from them. Have you checked for those?
 
  • #5
The simplest explanation is that there is a small amount of impurity, but it is a strong x-ray scatterer so there are large peaks in the measured spectrum.

Remember that the peak height only indicates the relative mass fraction if the scattering power of the compounds being compared are the same.

If you put a small amount of transition metal in graphite you'll primarily see the metal peaks.
 

What are unexpected peaks in XRD?

Unexpected peaks in XRD refer to peaks that appear in a diffraction pattern that are not expected based on the known composition of the sample. These peaks can indicate the presence of impurities, phase transformations, or instrumental artifacts.

What are some possible causes of unexpected peaks in XRD besides doping?

Aside from doping, unexpected peaks in XRD can be caused by sample contamination, preferred orientation, strain, and instrumental errors. Sample contamination can introduce impurities that may cause peaks to appear in the diffraction pattern. Preferred orientation, or the orientation of the sample crystals, can also lead to peaks that may not be present in a randomly oriented sample. Strain, or the distortion of the crystal lattice, can also result in additional peaks. Finally, instrumental errors such as background noise, incorrect instrument calibration, or sample preparation errors can also cause unexpected peaks.

How can unexpected peaks be identified and distinguished from true peaks?

To identify and distinguish unexpected peaks from true peaks, it is important to carefully analyze the diffraction pattern. This may involve comparing the pattern to known reference patterns, looking for additional peaks in other areas of the pattern, and performing further analysis techniques such as Rietveld refinement. Additionally, understanding the sample composition and potential causes of unexpected peaks can help in identifying and distinguishing them from true peaks.

What are some methods for preventing or minimizing unexpected peaks in XRD?

To prevent or minimize unexpected peaks in XRD, it is important to carefully select and prepare the sample. This may involve ensuring the sample is free of impurities and properly ground to a fine powder. Additionally, using a randomly oriented sample and carefully controlling instrumental parameters, such as beam intensity and wavelength, can also help to minimize unexpected peaks. Regular instrument maintenance and calibration can also prevent instrumental errors that may cause unexpected peaks.

What should be done if unexpected peaks are observed in XRD?

If unexpected peaks are observed in XRD, further analysis and investigation should be conducted to determine the cause of the peaks. This may involve comparing the pattern to known reference patterns, performing additional analysis techniques, and considering potential causes such as impurities or instrumental errors. It may also be necessary to repeat the experiment with a different sample or under different conditions to confirm the presence of the unexpected peaks.

Similar threads

  • Atomic and Condensed Matter
Replies
0
Views
1K
  • Atomic and Condensed Matter
Replies
2
Views
2K
Replies
2
Views
944
Replies
1
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
4K
  • Advanced Physics Homework Help
Replies
1
Views
5K
  • Quantum Physics
Replies
4
Views
692
Replies
2
Views
2K
  • Electromagnetism
Replies
17
Views
1K
Replies
1
Views
1K
Back
Top