intensities of peaks (111) (400) (422) (511) significantly increases with increasing the Mg doping concentration, why is so? any refrence to study please?
Probably enhanced grain growth, you should try to check the difference in the microstructure of these two ceramics whose XRD kyou have shown.
To answer specifically why it is due to Mg, is alittle difficult for me, but I definitely feel through could be differences in the grain size, densification, and microstructure.
K. Sreenivas
As written by K. Sreenivas you should have a look on your microstructure. In fact, chromites cannot show any increase af intensity if they will be doped by Mg since Mg has an even lover scattering factor. The lattice parameter obviously also does not remarkably change (densification) so that the only reason for your relative change of intensity can be only texture, i.e. a non-homogeneous distribution of crystal orientation. If I also interpret your data correctly both diffractograms have a different signal to background ratio. Is this correct? Or why the intensities for both phases is in general different (except of the obviously applied shift of the Mg-doped data)? Or did you also rescale the intensities? How did you performed the Mg-doping?
If we took Fe3O4 (Fd-3m) structure where:
Elem. X Y Z sof Wyck.
O1 0.24000 0.24000 0.24000 1 32e
Fe1 0.00000 0.00000 0.00000 1 16c
Fe2 0.37500 0.37500 0.37500 1 8b
Fe1 occupied octahedral site (six coordination) , Fe2 occupied tetrahedral site (4 coordination).
Neglected the electronegativity, substitution tend to occupied small space or small coordination. In this case Mg will substitute Fe2 before go to Fe1 after certain percent of substitution.
When we substituted Fe2, the corresponding planes that gave a positive contribution to the structure factor will increase in intensity, while the negative contribution will decrease in intensity.
If u compared by the increased intensity only, u must supply us with more details information such as instrument settings, sample (powder, bulk, film), sample preparation and diffractograms.
Pls take a look the simulation below, than compare the both patterns with urs. The intensity comparison between 111 and 002; before doped 111 is lower than 002, after doped it reversed.
In 111; Fe2 lattice is ~1/2 between 111, it gave negative contribution. If we reduce the scattering factor of this lattices by substituting with less electron such as Mg, the intensity will increase.
In 022/220; Fe2 lattice is ~1/4 close to 022/220 so it give positive contribution (opposite to 111).
All Fe1 lies at 004/400 and Fe2 lies in-between. Fe2 gave a negative contribution as well, so 111 and 004/400 increase while Mg substitution increase.
The intensities that are mainly involved are the 111 and 222. It could be such a situation: your pure ferrite has an inverse spinel structure while it seems that Mg doping can induce the formation of a regular spinel.
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