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

Abstract

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. ) 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 Na₄Mg₆Al₄Si₄O₂₀F₄·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.