How Do You Calculate the Lattice Constant Using Bragg's Law?

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Discussion Overview

The discussion revolves around calculating the lattice constant of a simple cubic lattice using Bragg's Law in the context of x-ray diffraction. Participants explore the implications of different diffraction peaks and the order of diffraction in the calculations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on using Bragg's Law to find the lattice constant, questioning what value to use for the diffraction order "n".
  • Another participant suggests using "1" for the first order diffraction lobe as the value for "n".
  • A participant questions the relevance of the diffraction peak, specifically asking if it matters if the peak was (422) instead of (222).
  • It is noted that "d" represents the spacing of the planes corresponding to the specific peak being analyzed, and that geometry may be required to derive the lattice spacing from the data.
  • A later reply discusses the relationship between the diffraction order and the Laue condition, indicating that higher order peaks may not be visible in standard setups and asserting that they are not necessary for the calculation at hand.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of the specific peak in the calculation and whether higher order peaks need to be considered. The discussion remains unresolved regarding the implications of using different peaks and the necessity of higher order reflections.

Contextual Notes

Participants do not fully agree on the implications of using different diffraction peaks or the necessity of considering higher order peaks, indicating potential limitations in their understanding of the geometry involved in the calculations.

vebbie
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need help working out this problem. if you have a simple cubic lattice characterised using x-ray diffraction with a wavelegth of 1.6\dot{A}. The main peak in the scan is (222) and the angle is 32 degrees. By using braggs law to find the lattice constant do you just sub in the values and solve for d? (n\lambda=dSin\theta. If so what value do you use for "n".
 
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It is the diffraction order, use 1 for the first order diffraction lobe.
 
but does the peak have any use for the calculation. suppos it was the 422 peak
 
d is the spacing of the (222) planes. If you were looking at the (422) reflection, then d would be the spacing of the (422) planes. You might have to do some geometry to get the lattice spacing from the data.
 
"but does the peak have any use for the calculation. suppos it was the 422 peak"

The index n is a consequence of the fact that reflections occur when (k - k') = G. Braggs Law diffraction condition is a simplification of the Laue Condition for diffraction: (k - k') = G. The higher order peaks are forward scattering instead of backwards scattering so you won't be able to see them in a standard diffractometer. You would nee to generate a Laue pattern to see these peaks. To answer your question you don't need these peaks.

modey3
 

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