Dear All,
I have some some confusing XRD patterns of Ni/C and Cu/C nanoparticles that I struggle to match with the known XRD cards or published patterns. I have some thoughts and questions that you may kindlky help with:
1. Would someone suggest a free software that I can use to analyze and accurately define those peaks?
2. How far is the accepted shift of diffraction angles for the same phase/material. For example the famous 25-deg C (002) peak is sometimes reported as low as 22 or as high as 28 with 6-deg diffreance. Is that ok? And what caues such a big shift?
3. Would somoene wish to collaborate by helping go deeper into analyzing our XRD patterns and elucidating some crucial info about the material structure?
Thank you,
Ahmed
Hello Ahmed Elsheikh
1 - Analyzes of XRD is done by Rietveld Refinement, which GSAS-II is one of many softwares that can do it. I recommend this because I think it is the easiest to learn from zero, and there are many tutorials available.
2 - According to Braggs' equation, a shift in the position of peaks is due to change in interplanar distance of crystallographic planes. Which means that if your peaks shift to higher angle, unit cell is shrinking, and if the peaks shift to lower angle, the unit cell is increasing size.
3 - I am willing to offer a deeper analysis of your results.
Best regards
Ricardo Tadeu
Thank you, Ricardo Tadeu Maia
1. Does the Rietveld Refinement accept.CPI files?
2. I know about Bragg's law and its associated diffraction angle shifts to lower or higher values. My question remains: Is there a maximum shift to the right or the left?
You see the hcp (002) phase is ideally located at 25 degrees. However, there are published works that report the same phase at as low as 22 degrees while others report it at as high as 28 degrees. Can this 5-degree difference be explained only by the lattice expansion/contraction?
Ahmed Elsheikh
1 - What is a CPI file? To make a refinement, we need the data file, and a CIF file (Crystallographic Information File)
2 - There is not a minimum or maximum value for a shift. We just have to make sure if it makes sense. For example, I don't know what should be the structure of these compounds you made (Ni/C and Cu/C), could you show how they should look like?
About the hcp: Think about graphite, which is a hcp crystal. I attached an image with its crystal structure. In red, the 002 plane. In green, 001 plane. You can see that graphite is made of layers of hexagonal carbons sp2. The distance from a layer to another is the 002 distance. You can deduce by chemical/physics intuition that this distance can vary.
Let's do math. What distance is 6 degrees, from 22 to 28 2theta in an experiment with copper Kalpha? Using Braggs law, the interplanar distance for a plane 002 in 22o is 4.11 angstrom. For 28o, interplanar distance is 3.28 angstrom. It's a difference of less than 1 angstrom of layer spacing. Pretty acceptable, isn't? So, this shift in 002 makes sense. But if 002 shifts, 001 shifts too.
Is everything clear now?
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