Interplay between Cation and Charge Ordering in La_1/3Sr_2/3FeO₃ Superlattices

Abstract

The electronic properties of digital superlattices are reported, which are cation‐ordered analogs of the perovskite La1/3Sr2/3FeO3, a material that undergoes a charge‐ordering transition. Superlattices of LaFeO3 (LFO), an antiferromagnetic insulator, and SrFeO3 (SFO), a conductor with a helical magnetic ground state, are fabricated via oxide molecular beam epitaxy. Three isocompositional superlattices with repeat structures of SSLSSL (S2), SSSLSL (S3), and SSSSLL (S4) (S = SFO, L = LFO) are studied with cation orderings along the [001] and [111] directions for experimental and computational work, respectively. The experimental superlattice structures are confirmed via synchrotron X‐ray diffraction and corresponding simulations of (00L) crystal truncation rods. The S2 and S3 superlattices are found to undergo an electronic phase transition as measured by a discontinuity in the temperature‐dependent resistivity similar to the random alloy, indicating that the superlattices do not behave as a simple combination of LFO and SFO. The charge‐ordering transition is not observed in the S4 sample. The electronic structure calculations using density functional theory, confirming the energetic favorability of charge ordering in the S2 and S3 structures compared to the S4 structure, are consistent with experimental trends.

Doping of BiFeO3 : A comprehensive study on substitutional doping

“…Such a combined reduction of Bader charges of oxidized metal centres and their oxygen surrounding has been observed previously. [89] These findings are in line with the mixed iron and oxygen character of the emerging acceptor bands. In addition to the discussed depopulation of two former VBs (direct doping effect) in one spin channel, we also observe a change in the iron dominated CBs in the other spin channel.…”

Charge-Order-Induced Ferroelectricity inLaVO3/SrVO3Superlattices

“…[6][7][8] In perovskite transition metal (TM) oxide (ABO 3 ) n (A BO 3 ) m (001) superlattices, the layered cation ordering lowers the symmetry from cubic to tetragonal and breaks up-down symmetry across BO 2 layers. Control of the TM d-orbital occupancy through choice of A cations and layer thicknesses to obtain a mixed valence leads to charge disproportionation and long-range charge ordering [9][10][11][12]. As we will discuss further below, layered charge ordering breaks the up-down symmetry across the AO and A O layers.…”

Superlattice-induced ferroelectricity in charge-ordered La 1/3 Sr 2/3 FeO 3

“…1C. Experimentally, (001)-and (111)-oriented thin films and (001)-oriented superlattices are reported, with resistivity measurements consistent with a charge-ordered Mott-insulating state as the low-temperature phase (28,29).…”

“…Charge ordering in LSFO has been the subject of investigation through first-principles calculations (26,(29)(30)(31), with disproportionation to Fe 3+ /Fe 5+ observed when on-site electron correlation is included via a Hubbard U parameter (30). These studies have considered various ordering patterns for La/Sr and their effects on charge disproportionation, charge ordering, and magnetic ordering of the electronic ground state (29)(30)(31). The energetics of the system are found to be driven by magnetic exchange, with both lattice distortion and correlation needed to produce an insulating ground state.…”