While calculating grain size, I have to calculate the uncertainty too. one of the parameters is dependent on the cycle of the lamp ( XRD source). I cannot find much information on this parameter. If anyone could explain what I should look for, it would be a great help. It is written that the parameter is related to the lifecycle of the lamp.
Dear Hala Achahbar ,
you may share the source, where it is written and what parameter is or may be related to the life cycle of the XRD source.
Nevertheless in the course of time the surface of the tube anode will be contaminated by a bit of Tungsten arising from W atoms emitted/evaporated from the filament.
The W L-alpha1&2 are at about 8,3 to 3,4keV. So they are only 300 to 400 eV apart from the Cu K-alpha line, which is used for XRD. In this case tiny structures may show up at the left side of the XRD peaks. But I do not know whether they are able to really lead to an increase of the FWHM values of the XRD peaks and thus to errors in the estimation of the mean crystallite*) size via Scherrer equation.
But I think, these lines are to low in intensity compared to the Cu K-alpha1,2.
In addition a Ni filter could help to reduce these lines. The energy position of the Ni K-edge is just below the energy positions of these lines.
With respect to 'Tungsten contamination' please see for example the section at the end of page 2 of:
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjKzraz4dTzAhXgh_0HHdXgDrcQFnoECAMQAQ&url=http%3A%2F%2Fbiophysics.fsu.edu%2Fsoma%2Fwp-content%2Fuploads%2Fsites%2F13%2F2015%2F11%2FPXRD-RadiationContaminations.pdf&usg=AOvVaw1_wcHQuNkKh9E8mCr_7WsW
*) by the way; with Scherrer equation you estimate the mean crystallite size, but not the grain size, as you noted above
That is another point , Steven Van Petegem .
But what do you think about whether tube life cycle affects on peak width some how?
That is the basic question here.
If so, then also the results via peak fitting methods will, to my opinion, propably suffer from tube aging.
Isn't it that LaB6 or any other standard should be measured before doing such measurements so this way one receives information about instrumental broadening so don't have to worry about the state of the lamp?
I agree with the doubts concerning the kind of unfluence of the X-ray source. My point is a different one and maybe provocative. In my view the Scherrer equation is correct, and basically the paper cited by Steven Van Petegem makes use of the Scherrer equation. The Scherrer equation is correct if you consider that the line width to be used in the Scherrer equation is the pure size broadening contribution (corrected for the the instrumental broadening and e.g. microstrain broadening, if present) and that the "size" value determined depends delicately from the size distribution and delicately depends on the crystallite shape (distribution).
All this has the consequence that some ad-hoc use of the Scherrer usually will give nosense (and the first time user will end up in degrees in the formula, giving even more nonses). But in my opinion, the Scherrer formula is correct if you are very specific about the meaning of the quantities contained in it. And this delicacy has the consequence that in practice much more advanced methods (like in the cited article) have been introduced to consider all this. But all these methods make use of the essence of the Scherrer formula.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction