I have already calibrated the diffraction instrument so I fixed the diffraction instrument and added two phases (Fe and Ni) and refined their volume fractions, cell lengths and isotropic (crystal size and microstrain). The problem I have is the refined weight fraction is not right and also data does not fit properly.
can anyone help me out of this?
I do not use Maud so maybe I can't help you very much, but looking at your diffractogram the problem seems to be with the intensities. Have you tried refining the preferred orientation parameter? This may help.
Yes. I used arbitrary texture and Delft line broadening model for both Fe and Ni.
You might try to fix all parameters except one. It seems like the fit is good but it has problem minimizing all the parameters involved. Since you milled Fe80Ni20 you might try forcing those weigths and the refine from there.
It appears to me that the peaks of the Ni fraction are calculated too broad. Maybe try a Pawley or LaBail fit first to check if the isotropic size strain makes sense.
Regards
Thank you for your answers. The fitting is better now but the problem is the peaks dose not fit properly more than shown in the figures, until unless I also refine Caglioti PV.
Caglioti parameters should be determined on the standard and kept fixed. Also, what kind of information do you need? Phase analysis, microstructure, unit cell parameters? Do you suspect presence of preferred orientations in your material? Though to me intensities look OK, so arbitrary texture may be redundant. And if you are trying to get volume fractions - arbitrary texture model would not allow you to do it correctly.
Since this is nanopowder, the use of "Distributions" model for the line broadening should help a lot. Also you may want to use more cubic shape of particles instead of spherical. But if you are interested in fine details of microstructure, I advise you to use PM2K. What do you think of diffuse peaks, e.g. the one at about 2theta=110 degrees?
Thank you for comment.
I am looking for crystalline size, crystallinity, lattice constants and phases.
There is not any peak in 110 degrees.
Then the workflow is straightforward. Make a GOOD calibration of the instrument. Use "Distributions" for the microstructure. Do not use arbitrary texture. If your fit is still not good, try it with the anisotropic grain shape and stacking faults models. Alternatively you could use PM2K software. Though it is not a Rietveld program, you can calculate structure factors manually, or extract them from MAUD, and afterwards input and fix them in PM2K. This way you will get volume fractions of Ni and Fe. Good luck.
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