it is in our knowledge that increased intensity is related to high crystallinity.my question purpose is to investigate the basic scientific phenomena of why the XRD intensity is related to crystallinity.
You do not post the card or the diffractogram. Do all the peaks differ in intensity or just one? The intensity depends on the nature of the atom(s) in the unit cell and the orientation of the crystal planes to the x-rays. If the particles are oriented slightly different or if there is some stage tilt then intensities may change. Try a rocking curve analysis and see if the intensities change. Your thesis that intensity is related to crystallinity is not strictly correct. Please post the diffractogram and card so we can see what is going on.