Peak shift will only be observed when there is a change in the lattice parameter. and broadening can also occur due to the lattice strain. So, if non of these thing happens I suspect that doping is not effective means Mn neither form any coherent bonding with the other components nor it substitute other elements to a level that can be dected by xrd.

ofcourse low percent can also be a reason.

XRD isn't effective when dopant concentration is very less as in your case. Try to use XPS or ICP, if available, and I believe that should work. Best of luck!

At very low loading xrd can't be useful but 5% doping is enough. You can check amount of Mn doped by ICP AES and as per comment by Yadav, peak shift or broadening can be observed.

For clear observation, take xrd of undoped and doped material on overlay mode.

First identify the marker peak for Mn which should be absent in MgAl2O4 and then check the marker peak area by changing doping conc. or else you can plot linearity by changing doping conc. of Mn.

Powder XRD will not be enough to qualitatively and quantitatively analyse Mn doping. If you have single crystals by doing single crystal XRD you might be able to see whether it is substituting in the Mg site or whether it is occupying interstitial space.

You can do ICP/AES or ICP/MS

SEM/EDS

or electron micro-probe analysis to get quantitative data.

1. As I understand, MgAl2O4 has the spinel crystal structure.

Some speculations can be made about your issue.

More or less ..it is possible to expect that Mn can substitute Mg(+2) or Al(+3) which are in tetrahedral and octahedral position in MgAl2O4. Manganese can incorporate into the latter as the Mn+2 or the Mn+3 ion.

2. We can compare all involving ion radii keeping in mind the ions coordination.

Mg(+2) - 71 pm in tetrahedral position.

Al(+3) - 67.5 pm in octahedral position.

Mn (+2) - 80 pm in tetrahedral position

Mn (+3) – 72 pm in octahedral position.

(for ex. Webelements.com)

In the simplest case, the Mn (+3) ion can go into the Al(+3) position. Less likely, the Mn (+2) ion can go into the Mg(+2) position. Both can be expected as substitutions. At the dopant concentration

of remarkable level you should see the XRD peaks’ shift to the low 2Ѳ in the case of uniform strains and the peaks broadening in the case of non-uniform strains in both cases. The shape of the peaks in these cases should be symmetric.

But one more case can appear if the dopant ions aren’t there exactly in substitutional positions

In this case you should analyze whether the peaks shape after doping process was changed to the asymmetric one.If so you observe distortions of crystal lattice.

The dopant concentration in your case is really very low. No shift and no broadening are observed. Please, try the last case with distortions.

First you have to compare the scattering power of the dopend. Mn has a twice that many electrons so that it effectively affects the intensity twice that strong compared to Mg and Al. The question is, where does it disappear? To find this out you have to follow E.M. Shishonok's advice. However, I would recommend to cross check the derived solution. Often, there are several explanations for a signal change like texture.

The answets from Yadav and all others are recomended for your question. For more information 5% additional of any element Or material to a compound does not produce a doping process but produce the alloy that’s if compound accepts a solid solution

mid not a second phase may be produced

if the alloy is made then an increase of lattice space may occur which can be detected by X-ray as well as for a second phase