Atomic-scale mapping and quantification of local Ruddlesden-Popper phase variations

TL;DR

This paper introduces a Python-based analysis platform that uses atomic-resolution STEM images to detect, quantify, and map local variations in Ruddlesden-Popper phases at the atomic scale, improving understanding of their structural heterogeneity.

Contribution

The work presents a semi-automated, statistically rigorous method for identifying and quantifying local $n$-phase variations in Ruddlesden-Popper materials using phase analysis of STEM images.

Findings

Enabled spatial mapping of local $n$-phase distributions.

Quantified intergrowth occurrences in layered materials.

Provided a robust method for analyzing atomic-scale structural variations.

Abstract

The Ruddlesden-Popper ($A_{n+1}B_{n}\text{O}_{3n+1}$) compounds are a highly tunable class of materials whose functional properties can be dramatically impacted by their structural phase $n$. The negligible energetic differences associated with forming a sample with a single value of $n$ versus a mixture of $n$ makes the growth of these materials difficult to control and can lead to local atomic-scale structural variation arising from small stoichiometric deviations. In this work, we present a Python analysis platform to detect, measure, and quantify the presence of different $n$-phases based on atomic-resolution scanning transmission electron microscopy (STEM) images in a statistically rigorous manner. We employ phase analysis on the 002 Bragg peak to identify horizontal Ruddlesden-Popper faults which appear as regions of high positive compressive strain within the lattice image, allowing us to quantify the local structure. Our semi-automated technique offers statistical advantages by considering effects of finite projection thickness, limited fields of view, and precise sampling rates. This method retains the real-space distribution of layer variations allowing for a spatial mapping of local $n$-phases, enabling both quantification of intergrowth occurrence as well as qualitative description of their distribution, opening the door to new insights and levels of control over a range of layered materials.