We have synthesized undoped and Fe doped La2O3 nanostrcutures. The crystallnity of La2O3 is increased by Fe doping. We also synthesized undoped and Fe doped SnO2 nanostructures. In this case, crystallinity of SnO2 decreased by Fe doping. Can any body please explain me the reason of this increase or decrease in crystallinity by Fe doping? The ionic radii of Fe is 76 pm, Sn is 71 pm and that of La is 117 pm. Does crystallinity vary due to change in ionic radii?
The crystal structure of an ionic system is affected by the size and the ionic charge of the dopant. This is an application of the radius ratio rule that is given in most textbooks on materials science.
Do you know whether the dopant is substitutional or interstitial in the lattices? If substitutional, does Fe substitute with a +3 oxidation state in the La2O3 and a +4 oxidation state in the SnO2? Do you realize, the ionic radii of the two oxidation states of Fe are different? What is your measure of crystallinity?
Dear Muhammad,
You need to specify your doping process. Are we talking about a doping in the ppm level or a 1-10% mixture which are also mistakenly referred as "doping"? Normally, you should not observe any significant change in the crystallinity if your doping is at ppm level however, if your material is a mixture at % levels, you might want to track some IR spectra in order to monitor what is the bonding situation of the Fe. Do they form solid solution? Or Fe is substituted with Sn in the first case and Fe enters the interstitial sites in the La2O3 case?
Otherwise, the doping process might involve some heating and this could create some changes in the crystallinity as well.
Thank you
The crystal structure of an ionic system is affected by the size and the ionic charge of the dopant. This is an application of the radius ratio rule that is given in most textbooks on materials science.
Do you know whether the dopant is substitutional or interstitial in the lattices? If substitutional, does Fe substitute with a +3 oxidation state in the La2O3 and a +4 oxidation state in the SnO2? Do you realize, the ionic radii of the two oxidation states of Fe are different? What is your measure of crystallinity?
The comprehensive answer provided by Dr. Ovecoglu is in the attached file.
Best wishes
@Civan Avcı Sir doping is definitely in % and not in ppm but I am talking about ionic radii in pm (picometer). Secondly, I've not obtained IR spectra of these sample yet and don't have knowledge wether doping is interstitial or substitutional. Thanks for your contribution to the problem.
@Jeffrey J Weimer Sir I don't have any idea yet whether doping is interstitial or substitutional in either case. A simple way to observe crystallinity (if I am not wrong) is decrease or increase in intensity of XRD peaks.
@Mehmet S Celik Sir I am very thankful to you as well as Dr. Ovecoglu for such a nice and detailed answer. Can you please provide some references of this reasoning for purpose of citation?
Dear Muhammad,
Thank you for your answer. The broadness of the peaks and the level of background signal in the XRD pattern will tell you about the crystallinity, not the intensity. The intensity usually differs when your crystals prefers to grow in some specific directions and not some others. Growth in those preferential planes correspond to the higher intensity peaks. In some cases, the intensity of the peaks can be different when you have simply different amount of material as well.
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