Suppression of ferroelectricity in ultrathin barium titanate films grown within mica-4 interlayer space

摘要

The critical thickness for ferroelectricity has assumed importance because of the integration of ferroelectric perovskite films into microelectronic devices. Recent calculations reported by Junquera and Ghosez (J. Junquera and Ph. Ghosez, Nature, 2003, 422, 506, ref. 11) have shown the critical thickness in the case of BaTiO3 thin films to be ca. 2.4 nm. We have grown BaTiO3 films of thickness ca. 1.2 nm within the crystal channels of sodium fluorophlogopite mica of chemical composition Na(4)Mg(6)Al(4)Si(4)O(20)F(4)center dot H2O. Dielectric permittivity measurements on the composites do not show any transition at 393 K. Several possible causes for the suppression of this dielectric anomaly have been examined e. g., reduction of BaTiO3, sodium ion introduction into BaTiO3 and generation of thermal stress on these films. All of these have been ruled out on the basis of available experimental data. We believe our results are consistent with the recently reported theoretical predictions.