In XRD diffraction peaks position for Zn2+ ions substituted Mn-ferrites are somewhat shifted to the left of the Zn0.25Mn0.75Fe2O4. Although, the materials exhibited two secondary phases (2θ = 33.3; 2θ = 35.6) develop by replacing pure diffraction peaks (2θ = 35.5).
Note:Figure XRD analysis of MnFe2O4, Zn0.25Mn0.75Fe2O4 and Zn0.75Mn0.25Fe2O4/PVP
peak shift may be attributed to
1- changes in stoichiometric composition by doping.
2- Instrumentations (Doppler effect during counts)
3- Microstructure parameters (crystallize size and lattice strain"
4- Thermal annealing
Dear R. Sagayaraj ,
in additon to the answers above I would like to add, that I think you know, that peak shifts are caused to changes in the lattice plane distances.
When replacing one kind of atoms by another kind of atoms in a lattice, such as in your case (Mn2+ replaced by Zn2+) there is in general a slight change in lattice constant due to the differences in the diameters of both types of atoms, unless no phase change occurs due to this replacement.
a) Increase of diameter will result in a slight increase of lattice constant and thus an increase of d-spacing, which will give a decrease in theta (peak shift to the left).
b) Decrease of diameter will result in a slight decrease of lattice constant and thus a decrease of d-spacing, which will give an increase in theta (peak shift to the right).
At look at the ionic radii *) will give:
Mn2+ low spin: 81pm
Mn2+ high spin: 97pm
Zn2+: 88pm
From this table, there we have in principle both possibilities of Mn replacements by Zn2+ according to case a) or to case b).
In your case mentioned above, when Mn is partly replaced by Zn2+, you observed a shift to the left; so case a) is valid: replacement by a larger atom (here by the Zn2+ ion). From the short list above, here only the Mn2+ low spin ion is the candidate, which can be replaced by Zn2+.
But unfortunately, I am not expert in electronic bonding.
Maybe an RG colleague may comment on which kind of Mn2+ ion is present in the Mn-ferrites.
*) table in https://en.wikipedia.org/wiki/Ionic_radius
Best regards
G.M.
I fully agree with Dr. Gerhard Martens, changes in interplanar distances can shift X-ray diffraction peaks. On the other hand, substitutional defects can also deform the structure.
R. Sagayaraj
I could observe there is also broadening of peaks. For example, look at the peak (220) and (400) in X-ray diffractogram (a) and (b).
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