How to address/sort out the issues while determining the instrumental broadening factor in X-Ray diffraction?
I would like to determine instrumental broadening in X-Ray diffraction. For this purpose:
1. I’m planning to run a slow scan, i.e., step size near the peak position as 0.01 ° for the reference sample and time per step = 2 s. Please suggest if this is okay or I can use a faster scan rate.
2. a) I’m planning to do this only for 2-3 key peaks at low angle (20-40 degree) and I’ll assume that only K-alpha 1 contributions are responsible for the source radiation. Please suggest if this approach will be correct.
b) Or else, I ‘m planning to adopt another approach. I’ll consider 2-3 key high angle peaks (50-80 degree) and since I hope to see 2 different peaks for K-alpha 1 and K-alpha 2, I’ll then select only those peaks for K-alpha 1 signal.
Out of approaches 2a and 2b, please suggest which one should I follow.
3. I’m planning to use the data for W-H equation to calculate βi in the following manner: (βi)n=(FWHMsample)n-(FWHMinst)n
Where FWHMinst will be calculated from the standard sample (LaB6, Si etc). Generally it is said that, 1
The instrumental broadening should be eliminated by deconvolution. please see this link for brief explanation....
https://www.springer.com/gp/book/9783540698555
You should certainly read up on the W-H method, as Poonam recommends. A few basic hints:
1. Do not (ever) assume only Kalpha1 is present! Use a computer program that will fit each observed peak to a sum of Kalpha1+Kalpha2 contributions defined by a single peak position (usually that of Kalpha1), width, height, etc. Any program designed for XRD analysis will do this, and there are lots of free programs. GSAS-II is a good option; even if you do not use it for Rietveld, it can do a good job of fitting all your peaks.
2. For W-H, use all peaks possible, not just low angle or just high angle. The more peaks the better. Just exclude peaks that overlap because they will have much greater uncertainties in width.
3. Collect instrumental broadening data over the full range of your data. Instrumental broadening will vary with angle.
4. Regarding n in calculating β, if you fit to Gaussian profiles, n=2. If you fit to Lorentzian profiles (same thing a Cauchy), n=1. If you use Pearson VII with variable exponent m* or Voight or pseudovoight, 1
Dear Boyer,
Thanks for your explanation. I have one more doubt related to this, "shall I assume broadening in the standard sample(Si, LaB6 etc.) is due to instrument only".
you may try this kind of approach:
Balzar, D., Audebrand, N., Daymond, M. R., Fitch, A., Hewat, A., Langford, J. I., Le Bail, A., Louë r, D., Masson, O., McCowan, C. N., Popa, N. C., Stephens, P. W. & Toby, B. H. (2004). J. Appl. Cryst. 37, 911-924. and many more like
Article Effect of processing parameters on microstructural propertie...
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