La-doped BaTiO3 heterostructures: Compensating the polarization discontinuity

Abstract

We demonstrate a route to manipulate the polarization and internal electric field of a complex oxide heterostructure using a layering sequence based on the LaAlO3-SrTiO3 interface. By combining sensitive atomic-level mapping of the structure using direct x-ray phase-retrieval methods with theoretical modeling of the electrostatic charge and polarization, we have devised a novel single-domain polar heterostructure. We find that ionic rearrangement results in strain and free energy minimization, and eliminates the polarization discontinuity leading to a two-fold increase of the spontaneous polarization towards the surface of an ultra-thin single-domain BaTiO3 film.

Three-dimensional atomic scale electron density reconstruction of octahedral tilt epitaxy in functional perovskites

“…Measurements on CaTiO 3 /NdGaO 3 , CaTiO 3 /DyScO 3 and CaTiO 3 /LSAT were performed at both room temperature and 30 K (at which all films are in polar state). A phase-retrieval algorithm (COBRA) is then employed to reconstruct the 3D electron density in real space 31 – 41 (See Methods and Supplementary Note 1 for experimental details). Figure 1d displays typical COBRA fits (orange solid lines) to experimental CTRs (blue dots) measured on CaTiO 3 /NdGaO 3 at room temperature.…”

“…Direct aberration-corrected scanning transmission electron microscopy (STEM) is now routinely used for probing atomic structures with picometers metrology; however, they probe the potential of two-dimensional projections of atomic columns, and deconvolving the information along depth direction is a challenge 22 , as we illustrate in this work. Coherent Bragg rods analysis (COBRA) 31 – 41 , which reconstructs 3D electron density with atomic resolution based on a phase retrieval algorithm taking advantage of the interference between the diffracted X-ray beams from the thin film and the substrate, is a promising technique for such purpose. COBRA requires no special sample preparation (such as in STEM) and is readily applicable to any epitaxial system with film thickness <20 nm.…”

High‐Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

“…[ 169 ] An alternative interfacial mechanism was found in a COBRA study by Kumah et al to be effective in allowing a polar monodomain BaTiO 3 film to develop. [ 170 ] A buffer structure of 1 uc LaTiO 3 /3 uc LaAlO 3 was grown between a 4 uc BaTiO 3 film and SrTiO 3 (001) substrate. A polarization mismatch occurs at the BaTiO 3 /LaTiO 3 interface in the stacking of charged planes along the (001) direction.…”