Combined theoretical and experimental study of the Moir\'e dislocation network at the SrTiO$_3$-(La,Sr)(Al,Ta)O$_3$ interface

TL;DR

This study combines experimental microscopy and computational modeling to analyze the structure and defect chemistry of Moiré dislocation networks at the SrTiO3-LSAT interface, revealing how dislocations influence local ionic states and defect formation.

Contribution

It provides a comprehensive combined theoretical and experimental analysis of dislocation cores at the heterostructure interface, elucidating defect chemistry and ionic states.

Findings

Dislocations cause undercoordinated Ta/Al cations and facilitate oxygen vacancy formation.

Reduced Ti$^{3+}$ is linked to dislocation structure and electron doping.

Ti diffusion into LSAT occurs with cation vacancies or Ta diffusion into STO.

Abstract

Recently a highly ordered Moir\'e dislocation lattice was identified at the interface between a \ce{SrTiO3} (STO) thin film and the (LaAlO$_3$)$_{0.3}$(Sr$_2$TaAlO$_6$)$_{0.7}$ (LSAT) substrate. A fundamental understanding of the local ionic and electronic structure around the dislocation cores is crucial to further engineer the properties of these complex multifunctional heterostructures. Here we combine experimental characterization via analytical scanning transmission electron microscopy with results of molecular dynamics and density functional theory calculations to gain insights into the structure and defect chemistry of these dislocation arrays. Our results show that these dislocations lead to undercoordinated Ta/Al cations at the dislocation core, where oxygen vacancies can easily be formed, further facilitated by the presence of cation vacancies. The reduced Ti$^{3+}$ observed experimentally at the dislocations by electron energy-loss spectroscopy are a consequence of both the structure of the dislocation itself, as well as of the electron-doping due to oxygen vacancy formation. Finally, the experimentally observed Ti diffusion into LSAT around the dislocation core occurs only together with cation-vacancy formation in LSAT or Ta diffusion into STO.