SLATER MODEL APPLIED TO POLARIZATION GRADED FERROELECTRICS

Ferroelectric thin films of BaxSr1-xTiO3 with compositional gradients normal to the growth surface have been formed by the successive deposi tion and annealing of films having step-variable Ba to Sr ratios. By s uitably tailoring the magnitude and sense of the gradient in Ba to Sr ratio, directional potentials can be built into the structures yieldin g a new, but controllable, hysteresis phenomenon. Slater's empirical m odel for ferroelectric materials has been extended to also describe th in films with polarization gradients normal to the growth surface, i.e ., graded ferroelectric devices. This model accounts for several aspec ts of these structures, including: the broadness of the permittivity p lots with temperature, the formation of a spontaneous potential upon o scillatory field excitation, offsets in the hysteresis graphs along th e displacement axis with directions which are gradient dependent, and the electric field dependence of that offset. (C) 1997 American Instit ute of Physics.