The variations of ferroelectric domain structures related to rotational striations and power striations are observed. The one-to-one correspondance between rotational striations and structures of ferroelectric domains have been demonstrated. The distribution of solute concentration in rotational striation is measured by means of energy dispersive analysis of X-ray in scanning electron-microscope, and we reached the conclusion that the ferroelectric domain structures are dependent on the gradient of solute concentration. The coupling of the spontaneous polarization with the gradient of solute concentration is experimentally demonstrated for the first time.