I have mad my sample where the Cobalt substitutes to the Strontium site in my sample. As Cobalt ionic radii is smaller than the Strontium, it is expected that the peaks should shift towards right side when doping% increases.
But in my case the peaks are shifting to the left side rather than the right side. Why is this so, and if it so, then how can we explain this behavior when writing a journal paper?
Can you give more information about your material? It would be unusual for cobalt to substitute for strontium in an oxide, for example, since their coordination geometries are quite different.
Catherine Ellen Rice, thanks for your reply. The compound is Sr5(PO4)3OH, i.e Strontium apatite.
Dear Anshul Sharma
Internal stresses can cause the crystal structure to expand. In particular, tensile stresses can occur when Co ions replace Sr ions. These stresses can cause the crystal structure to expand, increasing the interatomic distance, which causes the peaks to shift to lower angles (to the left). Such internal stresses can occur depending on the conditions of the doping process (e.g. temperature, cooling rate) and can lead to the structure being larger than the intended size.Did you do stress relieving annealing?
Kind Regards.
You might consider the Cobalt take the interstitial sites inside the structure since its ionic radius is significantly smaller than strontium.
It is possible that the cobalt substitutes for phosphorus in phosphate rather than occupying the Sr sites in the apatite lattice. That is the case for some other transition metal ions such as chromium or manganese in this structure. Since the ionic radius of cobalt in tetrahedral coordination is larger than that of phosphorus in PO4, that could be consistent with your results.
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