Lattice screening of the polar catastrophe and hidden in-plane polarization in KNbO3/BaTiO3interfaces

Abstract

We have carried out first-principles simulations, based on density functional theory, to obtain the atomic and electronic structure of (001) BaTiO 3 /KNbO 3 interfaces in an isolated slab geometry. We tried different types of structures including symmetric and asymmetric configurations and variations in the thickness of the constituent materials. The spontaneous polarization of the layer-by-layer non-neutral material (KNbO 3 ) in these interfaces cancels out almost exactly the "built-in" polarization responsible for the electronic reconstruction. As a consequence, the so-called polar catastrophe is quenched and all the simulated interfaces are insulating. A model, based on the modern theory of polarization and basic electrostatics, allows an estimation of the critical thickness for the formation of the two-dimensional electron gas between 33 and 36 KNbO 3 unit cells. We also demonstrate the presence of an unexpected in-plane polarization in BaTiO 3 localized at the p-type TiO 2 /KO interface, even under in-plane compressive strains. We expect this in-plane polarization to remain hidden due to angular averaging during quantum fluctuations unless the symmetry is broken with small electric fields.

Piezoelectric properties of ferroelectric perovskite superlattices with polar discontinuity

“…In the second of them, the ground-state structure is Cm(2). The discrepancy between our results and those obtained for the KNbO 3 /BaTiO 3 SL in [67] stems from the fact that the calculations in Ref. [67] were performed for the superlattice clamped on the SrTiO 3 substrate; at these boundary conditions, the P 4mm phase is indeed the ground state.…”

“…Until now, theoretical studies of superlattices with the polar discontinuity have focused on studying the distribution of polarization and electric field in these structures and on finding the conditions for the appearance of a two-dimensional electron gas at the interface [59][60][61][62][63][64][65][66][67][68][69][70]. The questions of the stability of the high-symmetry polar structure in such SLs, possible phase transitions in them, and the physical properties of low-symmetry phases were not analyzed.…”

Ultrahigh Energy Density of Polymer Nanocomposites Containing BaTiO3@TiO2 Nanofibers by Atomic‐Scale Interface Engineering

“…Plus, in addition to the out-of-plane polarization in [001] direction, the mutual occupation of Ba-Ti cations also gives rise to additional in-plane polarization as a result of the reduced constrain to the cation movement. [ 22,23 ] In the meantime, a larger dipolar moment could be induced by the increased tetragonality of BaTiO 3 as a result of the lattice expansion along the [001] direction. [ 24,25 ] In fact, interface engineering at the atomic scale has been adopted as a general approach to induce substantially increased electric polarization at the interface between two heterogeneous oxide thin fi lms.…”

Model of two-dimensional electron gas formation at ferroelectric interfaces

“…However, the non-stoichiometry of the simulated geometry implied that the interfaces studied in those works were metallic by construction. In fact it was later demonstrated 16 that since centrosymmetric KNbO 3 is polar with a formal polarization of half a quantum of polarization (modulo a quantum of polarization), just like LaAlO 3 , when a [001] interface between this material and a non-polar one is grown the ferroelectric polarization of KNbO 3 tends to compensate the polarity of the interface. As a result, the polarization of the KNbO 3 layer is pinned and its formal value in the ferroelectric ground state is approximately zero (up to a quantum of polarization) rendering any screening mechanism unnecessary.…”