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Unexpected peaks!

  1. Aug 31, 2009 #1

    drizzle

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    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
     
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  3. Aug 31, 2009 #2

    ZapperZ

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    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.
     
  4. Aug 31, 2009 #3

    drizzle

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    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: Aug 31, 2009
  5. Aug 31, 2009 #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?
     
  6. Sep 1, 2009 #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.
     
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