If I have 3 different dopants (Al, Ga, Li) in size and charge, can I use rule of mixture to determine the degree or magnitude of dopant based on size effect? I have read the paper about determination of doping magnitude by lattice parameter (a/c) in Wurtzite ZnO structure.
Journal of the European Ceramic Society 29 (2009) 1413–1418
Dear Sureeporn,
if you only had one dopant in your structure at any one time, determining its concentration via the resultant lattice distortion would certainly be possible if the effect of the dopant on the lattice parameters had been calibrated - such as Al in Wurtzite-ZnO in the paper you cite. However, if you have three different dopants, with potentially opposite or similar effects, this will not be easily possible. In your case, for instance, ionic size should increase in the following order: Li
Dear Max,
Thank you so much for you suggestion. This is the situation that I expected but I though I can distinguish by statistic analysis package but the analyzed data turned out to be too rough to draw a conclusion. At present, I used rule of mixture of each dopant and its concentration to make a correlation with lattice volume change. I got the correlation at polynomial R2 = 74% for 2nd order and 84% for 3rd order. However, I am not quite sure whether or not that seem sound scientifically. Please give me more idea. You are very welcome.
Hello, Sureeporn
Are there secondary phases with increasing concentration of dopants in the XRD results? As far as i know, for ion-doped ceramic materials, in general we would prefer to obtain single phase with increasing doping contents.
hope that it is helpful to you.
Good luck!
Best.
Dear Bo,
There is no second phase was detected meaning that it successfully got into the lattice. Now I found that the aspect ratio changing can indicate the magnitude of doping in certain degree (R2 > 75% compared to size-concentration effect which calculated by Rule of Mixture). Thank you for your help.
Oh this is a tricky problem, particularly because you have to consider vacancies formed by the dopants as well. Rietveld refinement of your diffraction data is a way to get at it but since you have so many variables and one of your atoms is Li (with little x-ray scattering cross-section), the problem will likely be under-constrained. You can get around this by adding in more data sets. Neutron diffraction would help with the Li and x-ray/neutron pdf analysis would give you more data sets but it might be over kill depending on what you are trying to do exactly.
If all you want is the chemical composition, ICP might get you there. You can't measure the oxygen content directly but if you can dissolve a large amount of powder, you can get a reasonable estimate assuming charge neutrality with the rest of your ions. Of course the powder would need to be phase pure since ICP can't distinguish between multiple phases.
As mentioned above, EPMA could be a good option too if you have more than one phase.
I agree with Travis, Rietveld refinement of diffraction data is the way to go. As he mentioned Neutrons will give you better contrast with Li (and oxygen as well, if you want to see if there are oxygen vacancies). You can also do anomalous scattering with x-rays by measuring just above and below the absorption edge you need to get better contrast on. Rietveld refinement programs allow you fit multiple diffraction patterns taken with various instruments and energies simultaneously, which will give you the best result for the occupancies of each atom on each site (including vacancies).
Thank you for all your answer. Now I am doing the research on the possibility to use Neutron to specify the defect or cluster. However, the quality of my thin film is still very low. It may cause some variation.
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