How can we determine the amorphous to crystalline ratio in an XRD pattern? How precise is the proposed method?
Hello
I am sorry but I dont know alot about this issue in XRD. But we have recently done some experiments using near edge x-ray absorption spectroscopy to determine cristallinity in TiO2 nanolayers. This seemed to work pretty well... what kind of material and thickness are you interested in?
If you have crystalline and amorphous states of the same material with the same composition and also with the same local structure then the problem is simpler. You will then have sharp Bragg peaks corresponding to the crystalline phase and also broad bumps under the peaks. If you could fit these peaks with some functions and get the integrated intensities then the ratio of the intensity of sharp peak to that of the broad peaks will give you roughly the mass ratios of the crystalline to the amorphous phases. Now if you have measured the diffraction pattern to a high value of sintheta/lambda and also determined the diffracted intensity of the empty sample holder then you can have diffraction data from the sample only by subtracting the background. Then you can make structure models and refine the crystalline and the amorphous phases at the same time with variable mass ratios that you can refine. Mind that this quantitative work will be very difficult. But you may succeed if the structures of both the crystalline and amorphous phases are already known. The job will be practically impossible if you do not have any knowledge of the structure beforehand.
Philipp: I am looking for bulk samples, although we can cut thin slice of that. It is a conductive semiconductor. How would be the near edge x-ray absorption spectroscopy's data? What are the limitations for that measurement?
Amin, you can do it calculating the integrated intensities. If your phases are known, you could use the software EVA or Topas from Nruker to do it easily. Search in google "crystallinity degree Topas or Eva, you can found tutorials.
I'm sure tou can use other software packages, but I use to use Topas or EVA.
The NEXAFS approach relies on a different "fingerprint" for the amorphous and the cristalline material. If there are significant difference in the NEXAFS spectra you can build up semi quantitative linear combination for unknown samples. Also for bulk samples, you will not be able to probe the whole sample due to absorption of the incoming and the outgoing x-rays.
First u need to build ur std background profile by using a known std sample (eg. SiO2, 10% glass : 90% crystalline) to extract ur constant background cts. That value then can be use to quantify ur sample.
In Rietveld analysis u can do by adding peak to fit the amorphous hump in std sample (eg. SiO2, 20% glass : 80% crystalline).
The deviation is about 1.5 - 3%, depend on data quality.
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