A ceramic product? Nanopowder?

In your question it is not clear which temperature are referring to ?

and what are you referring to as crystallite size

------------------------------------------------------------------------------

Normally grain size increases with increasing sintering temperature.

During sintering many crystallites of the same orientation coalesce togeher, and forma large grain having a certain orientation.

A conglomeration of many different grains (either of same size/different size), with eah grain having its own orientation, fomrs a polycrystalline solid , commongly known as a ceramic.

Grain size is seen through scanning electron microscopy on fractured/surface micrographs.

Crystallite size is normally estimated from the FWHM of the XRD peak and corresponds to regions of coherrent diffraction domain inside the material.

crystallite size can be either equal or less than the grain size.

A solid having a preferred growth and consisting of a single grain of a certain orientation is known as a single crystal.

K. Sreenivas

As I recall ...... The absolute temperature  is not the main issue as long as you  start above ( a bit !) the formatiom temperature   of the desired phase( look at its phase diagram , if it exists. The main trick for getting big cristallites is to hold the temperature just below the formation value and then cool increasingly slowly , to allow crystals to grow by annealing out  grain boundaries(dislocations)

not only temperature, but flow and pressure also influence the crystalline structures. at high temperatures re-flow may occur, impurities or trapped gases may come out; and atoms, which are not at minimum energy level , try to resettles. Adsorbed particles can diffuse on the as-deposited surface longer before they are immobilized by further incoming particles during deposition.

The answer which is given by Dr. K. Sreenivas is true the grain growth will take place with increase the sintering temperature.

Regards

I am also struggling with the same question in case of ferrites at 400C and 600C.