Superlattice-induced ferroelectricity in charge-ordered La _1/3 Sr _2/3 FeO ₃

Abstract

Charge-order–driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La1/3Sr2/3FeO3 (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 μC/cm2, a significant value arising from electron transfer between FeO6 octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order–induced ferroelectricity.

Surface triggered stabilization of metastable charge-ordered phase in SrTiO3

“…Furthermore, the nature of symmetry breaking in the CO phase enables to induce of ferroelectricity, even multiferroicity [7][8][9] , making it more attractive for device applications. While the precise microscopic mechanism of CO formation remains under intense scrutiny, the presence of intrinsic electronic instabilities concomitant with structural distortion is widely accepted for the critical boundary condition to stabilize CO phase 10,11 .…”

Polar Perturbations in Functional Oxide Heterostructures

“…[333] Likewise, it would be indeed plausible to transform non-polar centrosymmetric metals/semiconductors/superconductors/dielectrics to metastable polar non-centrosymmetric phases by using polar perturbation techniques (e.g., the polar proximity effect described in the Chapter 2) through thin-film heteroepitaxy. [40,228,333,[364][365][366][367][368][369][370] An emerging fundamental question is how to switch off-center displacements in polar metals. [327,334,[340][341][342]355,[371][372][373][374][375] In a metal, an electric field is perfectly compensated by free charges and there is no electric flux with zero net charge leading to the absence of an effective electric field.…”

Novel Functionality in Switchable Polar Materials

“…Additional candidates for charge-ordered ferroelectrics or antiferroelectrics have been identified in the SrVO 3 /LaVO 3 1:1 superlattice [24] and in La 1 /3Sr 2 /3FeO 3 . [25] The charge-ordered ferroelectrics offer the possibility of switching on electronic rather than lattice time scales, but realization requires examination of the nature of polarization switching in charge-ordered ferroelectrics and the role of the lattice. A recent investigation [101] shows that the coupling between the charge ordering and the lattice determines whether a given charge-ordered ferroelectric candidate system will be switchable; this analysis highlights the role of structural complexity and correctly predicts the experimentally observed switchability of magnetite.…”

“…Alternatively, ferroelectricity that results from charge ordering that breaks the symmetry to a polar space group, competing with nonpolar charge‐ordered states, has recently been the subject of increasing interest with new materials realizations. [ 23–26 ] Including the possibility of having either or both states be metallic increases the types of functional behavior yet further. In all cases, the fact that the states are not symmetry related, and therefore need not be exactly equal in energy, introduces the need for tuning, through composition, epitaxial strain, or picoscale interface control, to bring the system to the phase boundary and allow dynamic switching by applied fields or stresses.…”

“…Similarly, systems with two or more distinct (non-symmetry-equivalent) polar states, which include the "quadruple-well" ferroelectric CuInP 2 S 6 [22] are expected to exhibit analogous functional behavior.Alternatively, ferroelectricity that results from charge ordering that breaks the symmetry to a polar space group, competing with nonpolar charge-ordered states, has recently been the subject of increasing interest with new materials realizations. [23][24][25][26] Including the possibility of having either or both states be In research on functional materials, the focus of attention has increasingly shifted from ferroelectrics, with electric-field-driven switching between two or more symmetry-related insulating polar states, to materials with functional behavior based on the competition of antipolar and polar states, or two or more symmetry inequivalent polar states, with switching driven by applied electric fields and/or stresses. When the competing states are not symmetry related, they can have quite distinct magnetic, optical, transport, and topological properties, with functionality derived from modulating these properties or even turning them on and off.…”