First-principles study of competing ferroelectric and antiferroelectric instabilities inBaTiO3/BaOsuperlattices

Abstract

We report a first-principles study of ͑BaTiO 3 ͒ m / ͑BaO͒ n superlattices for a wide range of periodicities m / n. We show that such a system develops a polar zone-center instability for sufficiently large m / n ratio, which can be understood, at least qualitatively, from a simple electrostatic model and should lead to a ferroelectric ground state. However, the analysis of the phonon-dispersion curves also points out the appearance of stronger antiferroelectric instabilities at the zone boundaries around m = 4, before the critical ratio for ferroelectricity is reached and which still dominate beyond it. The dominant character of the antiferroelectric instability is explained from the depolarizing field which hardens the ferroelectric mode. This analysis allows us to predict that, ͑BaTiO 3 ͒ m / ͑BaO͒ n superlattices should present an antiferroelectric ground state for m larger than 4, which should smoothly evolve to a multidomain structure for increasing m values and only become ferroelectric for large m.

Ground‐state structure of KNbO3/KTaO3 superlattices: Array of nearly independent ferroelectrically ordered planes

“…In stress‐free BaTiO 3 /SrO superlattices, the in‐plane polarization appeared in SLs with the BaTiO 3 slab thickness of n ≥ 4 unit cells; when these SLs were epitaxially grown on SrTiO 3 substrates, the polar structure transformed to antiferroelectric (domain‐like) structure in which out‐of‐plane polarization alternated along [100] or [110] directions in each of BaTiO 3 slabs. This antiferroelectric structure was studied in more detail in BaTiO 3 /BaO superlattices grown on SrTiO 3 substrate 42. The instability at X point of the Brillouin zone appeared in structures at a thickness of BaTiO 3 slabs of 2–3 unit cells while the zone‐center ferroelectric instability appeared only at n = 4–5 unit cells.…”

Ferroelectric/paraelectric superlattices for energy storage

“…Antiferroelectric phases were measured in KNbO 3 /KTaO 3 and SrTiO 3 /BaZrO 3 24 superlattices, though the former present scant thermal stability, and the latter display antiferroelectricity for very thin layers. Theoretical works have predicted the appearance of antipolar states in BaTiO 3 /BaO superlattices 25 (though the electric field response was not computed) or electrostatically engineered ferroelectric thin films 26 (which display small stability regions). Still, the measured or predicted stability windows in these systems are rather narrow, leaving little room for optimization.…”

Influence of dielectric stiffness, interface, and layer thickness on hysteresis loops of ferroelectric superlattices

“…13 On the other hand, a recent study using first principle calculations reports that the internal electric field plays an important role in the appearance of antiferroelectricity (ground state) in ferroelectric/dielectric superlattices. 17 During recent years, numerous experimental studies have been devoted to investigate the ferroelectric properties of various superlattice or multilayer structures such as BaTiO 3 / SrTiO 3 , 18 BaTiO 3 /CaTiO 3 , 19 SrTiO 3 /BaTiO 3 /CaTiO 3 , 20,21 BaTiO 3 /LaAlO 3 , 22 BiFeO 3 /SrTiO 3 , 23 PbTiO 3 /SrTiO 3 , [24][25][26] as well as system involving relaxor ferroelectrics. 16,27,28 Majority of these works reported the observation of completely new or enhanced behaviors that are absent in the individual constituent.…”