MY sample is iron oxide doped with Zn and the lattice parameters I have determined from the Rietveld analysis. While the ionic radius of Zn is more than Fe, I found that compare to pristine sample the doped sample has decreased lattice parameters. PLease let me know if something I am missing here. Please note that the samples are hydrothermally grown and are not annealed.
Hi, as you stated, in principle, the lattice parameter should increase when you dope the material with larger atomic radii. The empirical formula Vegard's law dictates the same.
However, what you observed is also likely and appears in many cases, especially if the doped material or the material in which you are introducing the dopant changes its oxidation state.
Fe often shows mixed oxidation states +2 and +3 (mainly). With Zn doping, it is likely that some weight fraction of Fe changed its oxidation state (lower to higher, +2 to +3), thus decreasing the lattice parameter of the doped material.
Please take a look. Here are some examples, where in principle the lattice parameter should have increased, however, authors noted a contraction in the lattice due to the change of oxidization state of Fe in the first case, and Cu in the second.
1-https://doi.org/10.1063/1.5065074
2-https://www.nature.com/articles/srep32501
Hi,
From my point of view.
Sometimes doping not only creates interstitial (which might increase the lattice parameter for bigger ions via creating tensile force) but also can facilitate other kinds of defects too, like vacancies and complex state defects. You can try to perform PL to identify the defect states and compare them with both samples. This could help you to understand.
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