I have prepared TiO2 nanoparticles (solgel) at annealing temperature 300C , 400C, 500C, 600C. At 300C and 400C anatase phase observed as the temperature increases peaks becomes sharp. At 500C, 600C ,we observed mixed anatase+rutile phase.
Why peaks at 300C is less sharp and particle (300 to 600C) size is increasing with temperature?
Hi Neetu,
Initially I was surprised after reading your answer that you even managed to get clean XRD peaks at 300 C. But I remember now that there are indeed some acid-digestion methods that allow calcination at lower temperature.
Coming back to the question. In order for an amorphous material to form crystalline structure you need to provide sufficient energy to allow mobility of the constituent ions. Same is true with titania. Crystal formation lowers the overall energy of the system and provides stability. The higher the temperature the better will be the mobility which results in formation of larger crystals. However, I suspect in this case it just leads to complete crystallization instead. Thats why you get sharper peaks at higher temperatures.
The second part relates to phases. There is ample literature on temperature-related stability of titania phases (anatase, rutile, and brookite). Briefly, different phases are stable at different temperatures and phase-pure or mixed-phase materials can be prepared by careful control of synthesis parameters. Please look it up. In your case a DSC analysis of the amorphous powders should be enough to identify these transition temperatures.
Thirdly, the particle growth that you are observing at higher temperatures could either be coalescence or sintering. Essentially, each chemical system wants to minimize its overall energy, and atoms at the surface have a higher energy than those in bulk. By extension smaller particles have larger surface area and a higher energy. Therefore, if given the chance the smaller particles would like to fuse together to form bigger particles and lower the overall energy of the system. This happens when the temperature is high enough to enable long-range mobility.
This is all a very general explanation. I encourage you to read further as all these topics have been rather well documented.
I hope it helps.
You can even look through some of my papers for reference. However, for a more detailed explanation I recommend reading the following: https://pubs.rsc.org/en/content/articlelanding/2018/ra/c8ra06517a#!divAbstract
Dear Dr. Neetu:
A time ago, I answer a question at about TiO2 synthesis. If you might, please read the mentioned answer:
https://www.researchgate.net/post/Is_there_any_relationship_between_annealing_temperature_200-650_and_XRD_peak_shift_d_spacing_and_particle_size_for_the_dominant_anatase_peak
It is natural the evolution of broadness and intensity of diffraction lines. In fact, the major mechanism operational is the classic grain growth. In fact, crystallite growthing allows the decreasing of defect concentration and its distribution that are major contribution of stress/strain at crystallite. This event is called of crystallization, since diffraction lines reach to intense and very sharp profile. In practice, as a matter of fact, nanometric and submicrometric particle exhibit major part of defects at surface. In a thermodynamic view, the great surface energy is a driving force at crystallite growthing. However, the phenomenon is or can be modulated by heating rate, atmosphere, temperature, agglomeration state, etc...
With best regards
Marcos Nobre
Dear Dr. Rathore:
Then, during heating the particle growth to decreasing the energy of surface from one or more mass transport actuation, bulk diffusion, grain boundary diffusion and surface diffusion depending on the temperature and size reach.
With best regards
Marcos Nobre
You can have a look at some of my articles here on RG.. I have done some Raman temperature dependence studies on TiO2..
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