This is my first time dealing with XRD and I would like to calculate the crystallinity of my sample using powder XRD, I was trying to use the segals equation but I am not sure if its the right one for my sample, particularly because my peaks are not in the 2Theta region usually used for this equation, wherein max intensity peak is between 22-24 degrees and the amorph is taken at an angle of about 18 degrees in the valley between the peaks.
The sample is cellulose which initially had peaks in the regions mentioned above ,however, after regeneration the peaks shifted, crystalline at around 13 degrees and amorph at around 18 degrees. Just to see I calculated the crystallinity using the Segals equation but the values are way too high for regenerated cellulose indicating that this is probably not the right way to do it
The XRD graph is attached (sample holder was glass, which is why theres quite a bit of noise). Can someone please advice how else I can calculated the crystallinity from the XRD.
You also need to subtract the scattering from an empty sample holder. Your sample looks very amorphous. There is sign of a peak around 23.5, bout you'll need much better signal to noise ratio to get a meaningful result.
Thanks for the replies,
Mr. Oien I already did subtract the background reference from the result. Could you suggest how to improve the signal to noise ratio?
In general, you can fit your powder pattern with a program that perform Rietveld refinement and from the ratio between the area of crystalline phases (if there are known their crystal structures) and the area of amorphous one you can obtain the % of crystallinity. Otherwise you can add a known amount of a standard and perform again a Rietveld refinement in which you suggest to the program the known amount of the added phase and it will be able to determine the amorphous (for example Topas of Bruker)
Amorphous phases cannot be detected directly by X-ray diffraction analysis, because they do not produce additional visible reflexes in the X-ray diffraction diagram, but only increase the background. The reproducible quantification about 20 - 80% for a standard instrument. But in case of nanocrystalline phases present, than background determination will be more complicated (diffuse scattering).
Use spiking method to calculate the amount of amorphous phase if u know the all the phase present. I usually use 20% of NIST Al2O3. Once u did the refinement the Wt% amorphous = 1 - (Wt% Al2O3 added / Wt% Al2O3 refinement), finally normalized the original component without Al2O3.
"Amorphous phases cannot be detected directly by X-ray diffraction analysis". Only if you are handicapped by conventional XRD tools and techniques :-)
However, Maykel is right in the sense that precise quantification of a mixture of amorphous and crystalline phases is not a trivial task (may be impossible) with a conventional equatorial diffractogram that your are presently using. Having said that, it is quite common practice to estimate the relative amounts of such phases in samples using carefully created "known standards" when possible. It would also require careful and consistent sample preparation in this case. There are many more factors that may cause errors such as diffractometer alignment and sample surface alignment co-linear with the diffractometer axis (see attached RG discussion). Besides, amorphous/crystalline phase combination would invariably be accompanied with the ubiquitous "preferred orientation" monster :-). See attached image with Aluminum foil and Kevlar fibers.
For the time being just run and compare the diffractograms for various samples. Post the data. You may subsequently be able to compute integrated intensities below constituent peaks after identifying them and fitting them with the correct profile. This may be accomplished using many of the existing software. What XRD equipment are you employing? Please post details.
"Subtract" is a word I'd avoid in XRD. The better euphemism is "deconvolute" after unequivocal identification.
"how to improve the signal to noise ratio?". An excellent and practical question. Quick answer is, try a zero background sample holder (Si mono-crystal)! The full answer would depend on several of these enumerated factors:
P.S.: Please include additional relevant topics (up to 15) up top for enhanced circulation and improved feedback. Review the attached RG discussion regarding diffractometer alignment for a variety of such topics.
https://www.researchgate.net/post/What_is_the_conventional_alignment_procedure_critical_for_precision_in_XRD_for_sample_surface_positioning_collinear_to_the_diffractometer_axis?_tpcectx=profile_questions
Fatima Ahmad
Crystallinity index is the ratio of the crystalline peaks to the crystalline+amorphous peaks. Amorphous peaks are the noise in XRD data, while, from crystalline+amorphous, we mean the whole XRD profile. In the following 17 min video, I have explained in detail the crystallinity index and how to calculate it from XRD data. In the first 2.5 min, I have first explained 'what is meant by the crystallinity index'. In the rest of the video, I have taught 'how to calculate the crystallinity index from XRD data in origin for crystalline as well as amorphous materials. If you need anything further to ask, let me know. I'll appreciate your feedback on the video tutorial. I have attached the discussed files (Origin file and Excel template) here, as well as, they can be accessed from the description in the video. Thanks
How to calculate crystallinity index from XRD data using origin
https://youtu.be/D65k1yHPKaM
To get a sustainable solution to your problem, please refer to the preprint article given at link DOI: 10.13140/RG.2.2.27720.65287/3 or at link https://www.researchgate.net/publication/352830671.
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