Basically for Ag nanoparticles. 111 is sharp and single but 200 (44.29 and 44.41), 220 (64.45 and 64.62), 311 (77.37 and 77.60) are showing sharp, kind of equal intensity doublets.
This may be due to CuKalpha1 and CuKalpha2 of your X-ray source. The peak associated with Kalpha2 is smaller (ca. /2) and the separation of the two peaks increases with 2theta. This doublet is only detected when X-ray peaks are narrow. You may have a function in your X-Ray data treatment software that "strips" Kalpha 2
http://prism.mit.edu/xray/introduction%20to%20xrpd%20data%20analysis.pdf
Prasanna S. Ghalsasi,
Juliette Blanchard provided a decent answer, explaining the peak separation due to the Cu K-alpha splitting phenomenon. This also jives with the increase in peak separation you mention, increasing with 2theta, which is derived from differentiation of the Bragg equation.
One comment in the original question makes me wary; you mention that the peaks are similar intensity, where the K-alpha splitting should be a 2:1 Ka1 to Ka2 ratio. If this is in fact the case, you need to consider contamination, either from processing, preparation, or from your tube or other diffracting samples within the beam (steel components with sample holders etc.).
Good luck!
It's very interesting question. In addition to above scientific answer, I would like to give my comments. First of all if the doublet occur due to the ka1 and ka2, then it's effect need to observe for every peaks. The effect due to different wavelength can be easily cross check by calculation of 2theta value. You can use the n lamda = 2d sin theta formula. Where lamda is the wavelength. If you find the 2theta difference is more in your experiment case, then you can convince yourself that the peak splitting is not due to the ka1 and ka2 different wavelength, rather it could be due to the some impurity phase. Checking intensity ratio 2:1 corresponding to ka1:ka2 works very well in many cases. But it is rather dangerous in case of materials have nano structure. As with nanostruring case peak become more broader. The most intense peak generally found at lower angle nearly 30 to 40 degree. A possible solution is that you can use nickel filter to minimize the effect of ka2, but the intensity will be poor as diffracted beam reach to the detector through filter. The solution to improve the intensity is to use large amount of powder and scan very slowly, or repeated mode of scan untill signal to noise ratio become large. Third point, just anneal the sample for 1 or 2 hr at high temperature, where you make sure that sample change to bulk from nano. Repeat the experiment of xrd, you can easily figure out it's sample problem, ka1#ka2 problem or instrument problem. To confirm your instrument is working well, scan the standard sample e g silicon powder alone or mix with the samples to get your sample phase and silicon sample phase together. These are the many solutions you can try. If still the problem persist, and you are pretty sure sample is single phase then go for synchrotron measurements which use monochromatic beam. There is no trouble of ka1 and ka2 related issue. You can discuss with me any time for any kind of problem you have related to xrd. Good luck
My first reaction is the same as Juliette Blanchard's, this sound like Ka1-Ka2 splitting. But I am wondering a few things when reading your question: Are they really nanoparticles? If the particle size is small, the Ka1-Ka2 splitting should not be possible to see, since the grain size broadening is then much larger. What optics do you use?
Also, if the two peaks are of the same intensity as you write, it is not Ka1-Ka2 as mentioned above by Alec Ladonis.
Anyway, first quick check: do the measurement on a piece of single-crystal (say, a silicon wafer) and you should easily the the Ka1-Ka2 splitting
Thank you Drs Juliette Blanchard, Alec Ladonis, Saurabh Singh, Per Eklund, and Steven Van Petegem. After reading your anwers, I am attaching data to give you real picture. Please comment
Zoom in the peaks! from the document you attached is hard to say something. Ex on peak splitting due to bichromatic X-ray source you can find in Article Magneto-functionalities of La1-xAxMnO3 (A = K; Ba) synthesiz...
(Fig 2a).Also be careful to the alignment procedure, instrument function and integration time!
yes, we can't see anything in that pdf, but from the intensity list it can't be Ka1-Ka2 splitting as the two split peaks have roughly the same intensity.
Indeed, it's definitely not due to Ka1-Ka2. Could it not be due to the presence of another Ag phase? There are some reports of tetragonal Ag° phase under ambiant conditions for silver nanowire (see, for example:
https://www.nature.com/articles/ncomms1963?page=3)
Thank you Dr Steven Van Petegem, Dr Juliette Blanchard, Dr Per Eklund. It is not nano, and possible different phase of Ag0. Thank you. This will help me,
This effect may be due to the presence of cubic and hexagonal phases of silver. We observed such effect in
https://www.researchgate.net/publication/349361856_Influence_of_the_molecular_weight_and_concentration_of_PVP_on_the_polyol_synthesized_silver_nanoparticles
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