Ground‐state structure of KNbO 3 /KTaO 3 superlattices: Array of nearly independent ferroelectrically ordered planes

2020

Ferroelectrics

Self Cite

The stability of high-symmetry P 4mm polar phase in eleven ferroelectric perovskite superlattices with the polar discontinuity is studied from first principles. In most superlattices, this phase exhibits either the ferroelectric or the antiferrodistortive instability, or both of them. The structure of the ground state and, for a number of systems, also of metastable phases in these superlattices is found. The spontaneous polarization and piezoelectric properties of superlattices are calculated. The appearance of high piezoelectric coefficients (up to 150-270 pC/N) in some superlattices is associated with the strain-induced local rearrangement of certain atomic groups in the primitive cell.

Section: Resultssupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Piezoelectric properties of II–IV/I–V and II–IV/III–III ferroelectric perovskite superlattices

2020

Ferroelectrics

Self Cite

“…It is seen that in addition to the instability at the Γ point, the instabilities also appear at the X, R, and Z points of the Brillouin zone. We have already encountered a similar situation in KNbO 3 /KTaO 3 [42] and BaTiO 3 /BaZrO 3 [44] SLs. xy-polarized displacements of Bi and oxygen atoms lying in the same xy plane are stronger; this displacement pattern is characteristic of BiScO 3 .…”

Section: Search For the Ground-state Structuresupporting

confidence: 54%

Piezoelectric properties of ferroelectric perovskite superlattices with polar discontinuity

Computational Materials Science

2021

Self Cite

The stability of a high-symmetry P 4mm polar phase in seventeen short-period ferroelectric perovskite superlattices with polar discontinuity is studied from first principles within the densityfunctional theory. It is shown that in most superlattices this phase exhibits either the ferroelectric instability or the antiferrodistortive one, or both of them. For each superlattice, the ground-state structure, the structure of possible metastable phases, the spontaneous polarization, and piezoelectric properties are calculated. The properties of superlattices with the polar discontinuity are compared with those of superlattices with broken symmetry and of ordinary superlattices, which have no the polar discontinuity. It is shown that high piezoelectric coefficients (up to 150-270 pC/N) in some superlattices with the polar discontinuity are due to the appearance of strong lattice distortions, whose symmetry follows that of a low-lying polar phonon mode of the ground-state structure, under the influence of external strain.

“…A similar instability region along the path Γ-Z-R-X-Γ was observed in KNbO 3 /KTaO 3 superlattices. 5 Among the possible polar phases resulting from the condensation of the unstable E u mode at the Γ point, the Amm2 phase with polarization along the [110] direction has the lowest energy in (BaTiO 3 ) 1 (BaZrO 3 ) n SLs with n = 1-7. However, the phonon spectra of this phase ( Fig.…”

Section: B the Batio3/bazro3 Superlatticesmentioning

confidence: 99%

“…The recent studies of the ferroelectric instability in free-standing (KNbO 3 ) 1 (KTaO 3 ) n superlattices grown in the [001] direction showed that, with increasing n, the tendency to the ferroelectric ordering is retained in KNbO 3 layers with a thickness of one unit cell while the interaction energy between neighboring KNbO 3 layers exponentially decreases. 4,5 It was shown that at n ≥ 2 the ground state of the SLs is an array of ferroelectrically polarized planes whose polarization is concentrated in the KNbO 3 layer, is parallel to the [110] direction, and weakly interacts with polarization in neighboring layers. The use of such arrays of quasi-two-dimensional ferroelectric planes as a medium for the three-dimensional data recording can make it possible to achieve a volume recording density of ∼10 18 bit/cm 3 .…”

Section: Introductionmentioning

confidence: 99%

Properties of BaTiO3/BaZrO3 ferroelectric superlattices with competing instabilities

2013

Phys. Solid State

Properties of (BaTiO3)1/(BaZrO3)n ferroelectric superlattices (SLs) with n = 1-7 grown in the [001] direction are calculated from first principles within the density functional theory. It is revealed that the quasi-two-dimensional ferroelectricity occurs in these SLs in the barium titanate layers with a thickness of one unit cell; the polarization is oriented in the layer plane and weakly interacts with the polarization in neighboring layers. The ferroelectric ordering energy and the height of the barrier separating different orientational states of polarization in these SLs are sufficiently large to provide the formation of an array of independent polarized planes at 300 K. The effect of the structural instability on the properties of SLs is considered. It is shown that the ground state is a result of simultaneous condensation of the Γ15 polar phonon and phonons at the M point (for SLs with even period) or at the A point (for SLs with odd period); it is a polar structure with out-of-phase rotations of the octahedra in neighboring layers, in which highly polarized layers are spatially separated from the layers with strong rotations. The competition between the ferroelectric and structural instabilities in biaxially compressed SLs manifests itself in that the switching on of the octahedra rotations leads to an abrupt change of the polarization direction and can cause an improper ferroelectric phase transition to occur. It was shown that the experimentally observed zcomponent of polarization in the SLs can appear only as a result of the mechanical stress relaxation.