what may be the possible reasons of decrease in crystallite size at higher temperatures? I prepared TiO2 nanoparticles by sol-gel method and calcined at different temperatures but first its crystallite size increasing as temperature increased but further increase reduces crystallite size and then increased again. Any one can help me to explain the reason.
Are we talking about the same peaks? Is it possible that, at some calcination step you reach a phase transition temperature and your crystallinity weakens and, after the phase transition you recover the crystallinity?
The information given above is still insufficient, could you please mention using which technique you are determining the crystallite size? Are you assuming this on the basis of XRD peak broadening? or TEM analysis?
Is this phenomenon strongly reproducible following your exact protocol many times ?
Dear Mr. Kumar, I am using XRD peak broadening to fine out the crystallite size.
@ Mr. Cultrera I couldn't get your point. can you explain it to me?
Are we talking about the same peaks? Is it possible that, at some calcination step you reach a phase transition temperature and your crystallinity weakens and, after the phase transition you recover the crystallinity?
I mean, how many times did you repeat this same exact synthesis process ? Did you always encounter the same down-size effect ? Or in other words, how many batches of precursor did you started with the same results ?
I am of the opinion that this behaviour is due to some randomness in the measurements.
try to repeat your preparations, treatments and measurements. Come back to this question if you get same results again. Jacek
in one hand .the determination of the nanocrystal size by the XRD analysis depend on the (2 delta )value and the crystal plane. i prefer TEM analysis. in other hand ,the sol-gel method in the fabrication of the nanocrystal don't provide exactly the same size. so you must use TEM analysis to calculate the value of the nanocrystal size uncertainty .
TEM analysis is always best to see the particle size but Huang Wang is talking about crystallite size. TO see the crystallite size from Scherrer equation is not a bad idea.
Please do the phase analysis carefully. Probably at low temperature your samples have pure anatase phase, at moderate temperature a mix phase of anatase and rutile and at high a pure phase of rutile
please see the following reference
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8275331&fileId=S1946427411007597
I am of the opinion that the Sherrer formula for calculating the crystallite size has so many stringent conditions that usually it is wrongly used by young researchers, especially in developing countries, where complementary apparatus is not available. So tem is a relatively better option provided a good sample in a proper form is available.
I am not an expert but, as I understood, you perform the calcination of the samples at different temperatures, where the crystallization occurs, I suppose. In my opinion, if the phase analysis has been done correctly, what is going on is this: At low temperatures there is the formation of nanoparticles with just one crystallite, or in general small number of crystallite... (a nanoparticle can be a single crystal or can have more than one crystallite with grain boundaries between them).... so you note a certain value at XRD with Sherrer equation. Then, when you increase the calcination temperature, maybe the formation of more crystallite seeds is more probable, when the crystallization starts. This leads to the formation of some nanoparticles with more crystallites (and so more grain boundaries), that are smaller... Then, when you increase the temperature, those crystallites have the energy to sinter, and so you note the formation of bigger crystallites. Hope to have been clear.. But it's just an opinion, I can be wrong.. If I am not wrong, I think classic TEM is not enough to see this effects, and so, unless you have HRTEM, the best way is to use XRD.
Dear All,
Please note that it is not an answer, but is a SUGGESTION!
It is so clear and all of us know that TEM is better than SEM and it also is better than Scherrer's formula and/or Williamson-Hall method for particle and/or crystallite (or grain) size analyses. But the two first ones, especially the first one, is not so available for all and then someone has to refer to latter ones. Then I have a suggestion.
I think on the next step, now it is the time to use ResearchGate as a platform for installing new remote collaborations and developing researches with higher levels. Then if you agree, PLEASE VOTE TO THIS A GREEN MARK.
If you apply the Sherrer formula strictly according to the procedures laid down in BD Cullity's and Klug and Alexander's books then it can yield very accurate results.
My suggestion is that a Teaching Gate may be created where in detail discussions about issues relating to teaching and research may be exchanged.
Young fellows who are good at IT are requested to give suggestions. Privately I can be contacted at [email protected].
Totally agreed with Tahir Abbas, Scherrer equation is not that bad if we use it carefully. One can get accurate results even some time better than TEM as generally most of the researchers show a micrograph having only few particles, at the same time Scherrer equation gives us an average crystallite size. However, there are few thing which must have in mind.. instrument broadening and broadening because of strain in the sample.
You should repeat the preparation and check your furnace. I also suggest to determine the crystallinity of the powder. The crystallinity as well as size will increase with the temperature.
How to make it more clear that crystallite size and particle size are same or different? if there is some difference then there method to find out the crystallite size and particle size should be different. Can any one make it more clear to me. it is very confusing for me.
Some suggestions to read about crystallite size, particle size and grain size:
(1) For basic concepts: http://www.eng.uc.edu/~beaucag/Classes/Properties%20of%20Materials/MITCrystalSizeAnalysis.pdf
(2) For TiO2 particular case: https://www.researchgate.net/publication/270663300_Influence_of_sol_counter-ions_on_the_anatase-to-rutile_phase_transformation_and_microstructure_of_nanocrystalline_TiO2
Maybe your TiO2 is a misture of phases (anatase, Brookite and Amorphous material) as in (2).
BET and TGA/DTA analysis would give you some more information about your samples.
Article Influence of sol counter-ions on the anatase-to-rutile phase...
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles