PHASE-TRANSITIONS IN FERROELECTRIC-FILMS

The system considered is a ferroelectric film between metal electrodes with polarization normal to the interfaces. The critical temperature T(c) is depressed by the depolarization field, the film thickness l(c) for T(c) to be reduced to zero being or order 103 times the Thomas-Fermi screening length of the electrodes. For a film with no electrodes the ferroelectric phase is completely suppressed. The variation of T(c) with l > l(c) follows a simple hyperbolic law which should be open to experimental test.