[Paper Review] Effect of oxygen vacancy on structural, electronic and magnetic properties of La-based oxide interfaces

Urmimala Dey, Swastika Chatterjee+1 more|arXiv (Cornell University)|Jun 7, 2017

Electronic and Structural Properties of Oxides41 references3 citations

TL;DR

This study uses density functional theory (DFT) to investigate how oxygen vacancies (OVs) influence antisite disorder, structural distortion, electronic, and magnetic properties at La-based oxide heterointerfaces. It finds that OVs can either suppress or enhance antisite disorder depending on the specific oxide pair, enabling oxygen partial pressure to be used as a growth parameter to engineer interfacial disorder and stabilize desired electronic phases in oxide heterostructures.

ABSTRACT

Disorder, primarily in the form of oxygen vacancies, cation stoichiometry and atomic inter-diffusion, appear to play vital roles in the electronic and transport properties of the metallic electron liquid at the oxide hetero-interfaces. Antisite disorder is also understood to be a key player in this context. In order to delineate the roles of two of these key factors, oxygen vacancy and antisite disorder, we have investigated the effect of oxygen vacancy on the antisite disorder at a number of interfaces separating two La-based transition metal oxides using density functional theory. Oxygen vacancy is found to suppress the antisite disorder in some heterostructures and thereby stabilizes the ordered structure, while in some other systems it tends to drive the disorder. Thus by controlling the oxygen partial pressure during the growth, it is possible to engineer the antisite disorder in many oxide heretostructures.

Motivation & Objective

• To understand the role of oxygen vacancies (OVs) in modulating antisite disorder at La-based oxide heterointerfaces.
• To determine how OVs affect structural distortions, electronic structure, and magnetic properties in these systems.
• To identify which heterostructures are stabilized or destabilized by OVs, enabling predictive control of interfacial disorder.
• To provide a framework for engineering oxide heterostructures with tailored electronic and magnetic properties through growth condition tuning.

Proposed method

• First-principles density functional theory (DFT) calculations using the VASP code with GGA-PBE exchange-correlation functional.
• Incorporation of on-site Coulomb U corrections (GGA+U) for La-4f and transition metal 3d states with literature-derived U and J values.
• Construction of superlattice heterostructures of LaAO3/LaA'O3 with periodic boundary conditions.
• Calculation of antisite defect formation energy in both the presence and absence of oxygen vacancies.
• Analysis of octahedral volume distortions, charge density, and lattice strain to assess structural and electronic effects.
• Systematic comparison across 21 La-based oxide heterostructures (LaAO3/LaA'O3) with varying transition metals A and A'.

Experimental results

Research questions

• RQ1 How does the presence of oxygen vacancies affect the formation energy of antisite defects in La-based oxide heterostructures?
• RQ2 In which LaAO3/LaA'O3 systems does oxygen vacancy suppress antisite disorder, and in which does it promote it?
• RQ3 What is the role of lattice distortion and octahedral volume changes in stabilizing disordered or ordered phases in the presence of oxygen vacancies?
• RQ4 How do oxygen vacancies influence the charge density and covalency at the interface, particularly in Co- and Mn-based oxides?
• RQ5 Can oxygen partial pressure during growth be used as a control parameter to engineer antisite disorder and thus tune electronic properties?

Key findings

• In LaCoO3/LaCrO3 and LaCoO3/LaMnO3, oxygen vacancies increase octahedral volume standard deviation from 0.27–0.30 Å to 0.54–0.73 Å in CoO6 and 0.28–0.23 Å to 0.90–0.34 Å in CrO6/MnO6, indicating enhanced distortion and strain relaxation.
• For LaCoO3/LaCrO3, the octahedral volume difference between A and A' planes drops from 0.3782 Å (ordered) to 0.0412 Å (with OV), indicating stabilization of the disordered state.
• In LaNiO3/LaCoO3, oxygen vacancies reduce the standard deviation of NiO6 octahedra from 0.23 Å to 0.12 Å, indicating suppression of disorder.
• Oxygen vacancies enhance covalency at the interface, as seen in charge density analysis, which stabilizes antisite-disordered configurations in Co- and Mn-based systems.
• The presence of oxygen vacancies can either suppress or promote antisite disorder depending on the specific A and A' transition metal pair, with systems like LaCrO3/LaTiO3 and LaMnO3/LaCrO3 showing disorder suppression under OV.
• The study identifies 10 heterostructures where oxygen vacancies suppress antisite disorder (e.g., LaCoO3/LaCrO3, LaCoO3/LaMnO3), while 11 others show disorder promotion, demonstrating tunability via oxygen partial pressure.