Characterizing oxygen atoms in perovskite and pyrochlore oxides using ADF-STEM at a resolution of a few tens of picometers

TL;DR

This study demonstrates that aberration corrected STEM can visualize oxygen atoms in complex oxides at atomic resolution, revealing defects like vacancies that influence magnetic properties, and introduces a new method for resolving light atoms in such images.

Contribution

The paper introduces a novel quantitative ADF-STEM method capable of resolving oxygen atoms in perovskite and pyrochlore oxides at atomic resolution.

Findings

Oxygen atoms can be visualized in ADF-STEM images.

Point defects like oxygen vacancies are linked to magnetic ground states.

A new method enables quantitative analysis of light atoms in STEM images.

Abstract

We present an aberration corrected scanning transmission electron microscopy (ac-STEM) analysis of the perovskite (LaFeO3) and pyrochlore (Yb2Ti2O7 and Pr2Zr2O7) oxides and demonstrate that both the shape and contrast of visible atomic columns in annular dark-field (ADF) images are sensitive to the presence of nearby atoms of low atomic number (e.g. oxygen). We show that point defects (e.g. oxygen vacancies), which are invisible - or difficult to observe due to limited sensitivity - in X-ray and neutron diffraction measurements, are the origin of the complex magnetic ground state of pyrochlore oxides. In addition, we present, for the first time, a method by which light atoms can be resolved in quantitative ADF-STEM images. Using this method, we resolved oxygen atoms in perovskite and pyrochlore oxides.