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Ferroelectric phase transition; polarization; epitaxial strain; electrodes.

We determine the effects of film thickness, epitaxial strain and the nature of electrodes on ferroelectric phase transitions in ultrathin films of BaTiO₃ using a first-principles effective Hamiltonian in classical molecular dynamics simulations. We present results for polarization and dielectric properties as a function of temperature and epitaxial strain, leading to size-dependent temperature-strain phase diagram for the films sandwiched between `perfect' electrodes. In the presence of non-vanishing depolarization fields when non-ideal electrodes are used, we show that a stable stripe-domain phase is obtained at low temperatures. The electrostatic images in the presence of electrodes and their interaction with local dipoles in the film explain these observed phenomena.

J Paul¹ T Nishimatsu^{2 3} Y Kawazoe² U V Waghmare¹

1. Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India
2. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3. Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08544-8019, USA