Briefly speaking, relative intensites of the XRD peaks are mainly (but not exclusively) determined by the chemical composition and positions of the atoms in the unit cell and FWHMs (after subtraction of the instrumental contribution) are determined by the imperfections of the crystals, including small size and microstrains. Please, refer to the XRD textbooks for mathematical details.

Clays have strongly anisotropic layered structure, so I would recommend to pay special attention to the possible preferred orientation (will affect intensities), anisotropic size/strain broadening and stacking faults.

High relative intensity and narrow FWHM of clay  polymer system is related to well ordered of clay layer within polymer matrix (interlacalated structure) whereas  less orde

Thanks to both of you