Piezoelectricity Across a Strain‐Induced Isosymmetric Ferri‐to‐Ferroelectric Transition

Abstract

into applications ranging from ultrasound imaging technology to precision actuation in micromotors. [ 6 ] The recent discovery of a class of hybrid improper ferroelectrics (HIF), [ 7,8 ] where an electric polarization is driven by two coupled octahedral-rotation lattice modes, offer opportunities for design of ferroic materials with diverse functionalities. Typically, in A -site ordered ultra-short period 1/1 AB O 3 / A ' B O 3 perovskite superlattices exhibiting HIF, the electric dipoles of each cation sublattices are restricted by the symmetry of the orthorhombic a − a − c + B O 6 rotation patterns [ 9 ] in Glazer notation. [ 10 ] Such a rotocrystalline anisotropy stabilizes a ferrielectric (FiE) state, [11][12][13][14] where two of the three cation-sublattice dipoles are directed along the pseudo-cubic [110], while the third is anti-parallel to the others [110], yielding a net non-zero electric polarization. [ 15 ] In such a layered structure, the electric polarizations of each cation-sublattice can be tuned independently-the A and B cation polarizations directly rely on the octahedral connectivity of the system. [ 16,17 ] Is there a suitable way to tune the oxygen lattice topology and the polarization direction of each cation-sublattice? If answered in the affi rmative, then the FiE state can be directly converted into a FE state where all cation-sublattice dipoles are in parallel alignment. Consequently, a new FiE-to-FE ferroic transition would achieve a signifi cant polarization enhancement and a sizable piezoelectric response in cation ordered oxides.In this paper, we use fi rst-principles density functional calculations to demonstrate that the polarization switching between a FiE and FE phases in HIF AB O 3 / A ' B O 3 perovskite superlattices is accessible with substrate-induced epitaxial strain. Specifi cally, we uncover a fi rst-order isosymmetric phase transition and evaluate the feasibility of the FiE-to-FE transition through a minimum energy path (MEP) trajectory. Compared to perovskite oxide solid-solutions, where an enhanced piezoelectric response occurs near the MPB driven by rotation of polarization along an easy rotation path between the rhombohedral and tetragonal FE phases, [ 18,19 ] we predict a piezoelectric response-up to 102 pC/N around the FiE-FE phase boundary-as a result of the easy polarization switching between FiE and FE phases with the same symmetry. As A -site ordered superlattices or heterostructures, such as PbTiO 3 / SrTiO 3 , [ 7,[20][21][22] PbTiO 3 /CaTiO 3 , [ 23 ] and CaTiO 3 /BaTiO 3 , [ 24 ] have been successfully synthesized and well characterized in experiment, our predicted FiE to FE transition in synthetically We identify a fi rst-order, isosymmetric transition between a ferrielectric (FiE) and ferroelectric (FE) state in A -site ordered LaScO 3 /BiScO 3 and LaInO 3 / BiInO 3 superlattices. Such a previously unreported ferroic transition is driven by the easy switching of cation displacements without changing the overall polarization direction or crystallographic sym...

Improper ferroelectricity and piezoelectric responses in rhombohedral (A,A′)B2O6perovskite oxides

“…The out-of-phase rotations along all three crystallographic axes (in addition to rock salt ordering) removes all possibility for mirror symmetry but is compatible with threefold and twofold rotation axes. As previously reported for hybrid improper ferroelectrics, it is essentially the antipolar displacements of the different A-site cations which results in the electric polarization (a ferrielectric type mechanism) [18,45]. However, although out-of-phase rotations alone can lift inversion symmetry in [111]-ordered superlattices, the A-site atoms cannot displace perpendicular to any direction which contain out-of-phase rotations.…”

Colloquium: Emergent properties in plane view: Strong correlations at oxide interfaces

“…The link between the metallic layer and magnetism is best illustrated by studying superlattices where the metallic layer undergoes a metal-to-insulator transition when the dimensionality is reduced in the ultra-thin layer, and correspondingly the magnetism disappears (Grutter et al, 2013). One can use this understanding and exploit it to design new functional materials and there are many possibilities that exist within the perovskite familiy which can be combined to seek new types of magnetic states Gibert et al, 2012;Hoffman et al, 2013;Smadici et al, 2007). For example, many antiferromagnets have ordering temperatures well-above room temperature, so one could extend this concept to create interfacial insulating ferri magnets that operate at high temperature (Ueda et al, 1998).…”

Direct visualization of irreducible ferrielectricity in crystals

“…), which can be recognized as two uncompensated polar sub-lattices with antiparallel alignment 4,5 . In geometric ferroelectrics, such as Ca 3 Ti 2 O 7 and some perovskite superlattices, the displacements of ions are opposite between layers, which can also been recognized as two uncompensated dipole moments 6,7 . Despite the macroscopic and phenomenological analogy as shown in Fig.…”

“…By choosing different ions as a dipole unit, multiple dipole values for a sub-lattice can be obtained 8 . In this sense, the Cu-In pair in CuInP 2 S 6 or bilayer in Ca 3 Ti 2 O 7 can be treated as a dipole unit, which are indeed entangled simultaneously 4,6 . Therefore, these systems are indistinguishable from ferroelectrics, i.e., 'reducible' ferrielectrics, as qualitatively sketched in Fig.…”