How does doping in metal oxide change its crystal structure?
If you have a metal oxide and you start to substitute the metal ion in it with an other metal ion which forms isomorphous oxide, the crystal structure type will not be changed only the dimensions of the crystals (a,b,c,angles); however, if the size of the doping ion is different, and the substituting metal forms an other type of oxide, at a given level of doping the struture will be changed, e.g. from rhombic to monoclinic, etc., because the difference of forces due to size/charge ratio of cation and the size and space demand of the other metal ion, etc.
If you dope with a particular metal, two things might happen. There will be shift in the peaks of a Xrd pattern or there may be the formation of side phases.If the metal enters into the crystal lattice then we could see side phases, if not we could see the shift of peaks.
If you have a metal oxide and you start to substitute the metal ion in it with an other metal ion which forms isomorphous oxide, the crystal structure type will not be changed only the dimensions of the crystals (a,b,c,angles); however, if the size of the doping ion is different, and the substituting metal forms an other type of oxide, at a given level of doping the struture will be changed, e.g. from rhombic to monoclinic, etc., because the difference of forces due to size/charge ratio of cation and the size and space demand of the other metal ion, etc.
I also agree with above answer.
I will add few more points here.
1)Substitution or doping by other materials not only depends on the difference in ionic radii of the dopant and doped material but also other physical properties.
2)The percentage of doping is limited for most of the cases and depends on the dopant. For small doping concentration the crystal structure may be same as the undoped material but increase in the doping concentration can change the crystal structure or can resulted into other phase.
Doping implies that the added metal is incorporated into the crystal structure of the host rather than forming side phases. As mentioned by others, the dopant will affect the structure by expanding or contracting it based on the size differences and/or bonding (valence) differences, or possibly change the symmetry.
László Kótai What is the order of magnitude of the force generated by doping?
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