Formation of an amorphous domain pattern in type-II incommensurate ferroelectrics

Coarsening of a domain pattern during the cooling process in type-II incomm ensurate ferroelectrics like NaNO2 or thiourea is investigated in the frame work of two-dimensional discrete lattice model derived from the Ishibashi-S hiba potential. The cooling process is simulated by gradual change of the p arameters of potential with time. It has turned out that the resultant doma in patterns differ depending on the cooling rate. The present lattice model can satisfactorily reproduce the formation of lamellar and amorphous domai n patterns actually observed in NaNO2.