Why the Crystal size of bismuth ferrite decreases with cobalt doping [BiFe(1-X)CoXO3]; X=0.05, 0.1, 0.15
Hi,
provide more info about the structures you are using and the difference in lattice size, for example if you want to study the concentration x=0.1, it is better first to optimize 10[BiFeCoO3] structure, dope it, and redo the calculation with the same parameters.
Due to the smaller ionic radius of Co3+ ion than Fe3+ ion, lattice parameters decrease on doping of Co3+ at Fe3+ position.
I believe in your case structure is of perovskite type. You have to analyze it a little bit more carefully. First ensure oxygen stoichiometry is exactly 3. Fe as well as Co can have multiple (mixed) valence states as +2, +3, +4. Therefore, in addition to xrd it will be useful to take xps or XANES to extract what amount of Fe and Co are in which valence states. Compare their ionic sizes according the amount in similar coordination, in your case Fe and Co are in octahedral coordination with oxygen (if it is perovskite structure).
The atomic radius of Fe is 156pm while the Co radius is 152 pm. Despite this litte difference, one should expect the size to decrease with Co doping.!
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