Depolarization Field and Stability Considerations in Thin Ferroelectric Films

It is shown that the polarization in a thin ferroelectric film is always incompletely compensated. The associated depolarization field significantly modifies the phase stability of a ferroelectric film of sufficiently small thickness. For a slightly conducting ferroeletric film sandwiched between metallic electrodes, the polarization and transition temperature are depressed below the bulk values but the order of the phase transition remains unchanged. With semiconducting electrodes, even the order of the phase transition is modified for a thin ferroelectric film. A critical point exponent is calculated in each case within the framework of the Landau Theory. The results are compared and contrasted with the findings for other cooperative phenomena.