How to determine amorphous to crystalline ratio in an XRD pattern?
A simple way if you have relatively large amorphous and small crystalline is to use the 'measuring areas under the curve' method.
Take an area measurement that encompasses the amorphous and crystalline signals from a clear background position at low angle to a background position at high angle. Measure the area (cps x deg). This is the total area.
Model the amorphous background using background fitting. Use bezier curves and edit until you get a smooth line that mimics the wavy hump of an amorphous signature. Make sure the line goes through the center of the noise.
Subtract this amorphous background from the total scan to give only the crystalline peaks.
Measure the same area but this time on the crystalline only component.
Ratio the results: % crystallinity = (Area of crystalline / Area of total scan) * 100
The method breaks down with very small amorphous content as findng the correct background becomes difficult. It is then necessary to use internal standards and profile fitting/Rietveld quant as in the answer above. I have measure the same mixtures both ways and got similar results.
Just check the below link to get an idea.
http://www.ccp14.ac.uk/solution/gsas/files/expgui_quant_gualtieri.pdf
Crystalline materials cause sharp peaks visible in the XRD curve. Amorphous materials cause a wide bend in the baseline. The XRD analyzes act causing the reflection of x-rays in crystalline planes. The reflect of these plans are written in the form of peaks. Amorphous materials do not have crystal planes thus cause a diffuse reflection, which appears as a zigzag line basis with gentle undulation.
A simple way if you have relatively large amorphous and small crystalline is to use the 'measuring areas under the curve' method.
Take an area measurement that encompasses the amorphous and crystalline signals from a clear background position at low angle to a background position at high angle. Measure the area (cps x deg). This is the total area.
Model the amorphous background using background fitting. Use bezier curves and edit until you get a smooth line that mimics the wavy hump of an amorphous signature. Make sure the line goes through the center of the noise.
Subtract this amorphous background from the total scan to give only the crystalline peaks.
Measure the same area but this time on the crystalline only component.
Ratio the results: % crystallinity = (Area of crystalline / Area of total scan) * 100
The method breaks down with very small amorphous content as findng the correct background becomes difficult. It is then necessary to use internal standards and profile fitting/Rietveld quant as in the answer above. I have measure the same mixtures both ways and got similar results.
Using quantitative phases by the Rietveld method. The intensities integradasde reflections of one phase in a polycrystalline material are related to its abundance in the mixture (Klug and Alexander, 1974)
If amorphous phase or unidentified crystalline impurities are present in the sample, these percentages can be determined by adding a known amount (about 20%) of an internal standard.
with software GSAS - method Rietveld RIR ( you need of internal standard in the powder), you can quantify the weight percent of amorphous and the weight percent of crystalline phases. But it depends on how much you want to check the amorphous phase, L ' analysis usually has an error of 3%. The quantity of internal STD, change from system to system.
You may also want to check answers at a somewhat related discussion: https://www.researchgate.net/post/Could_anyone_explain_how_the_amorphous_content_of_a_material_is_analyzed_using_the_internal_standard_method_by_XRD
Studies of X-ray diffraction based on the Rietveld method allowing a quantitative study of a mixture of crystalline phases and amorphous phase (or crystalline unidentified impurities).
By so called transient cavitations mechanism.
www.fracturae.com/index.php/MST/article/download/1136/1088
Best regards
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