Atomic-Scale Visualization of Vacancy-Ordered Intermediates and Pathway Selection in the Perovskite-Infinite-Layer...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanoscale Dynamics

Background:

• Phase transitions in transition metal oxides are crucial for applications like ionic electronics and superconductivity.
• Understanding oxygen exchange mechanisms and transient intermediates in these materials is challenging.

Purpose of the Study:

• To resolve the atomistic dynamics of oxygen-mediated topotactic transformations in strontium ferrite (SrFeO_3-x).
• To identify transient intermediates and understand pathway selection during reduction and oxidation.

Main Methods:

• In-situ high-resolution transmission electron microscopy (HRTEM).
• Molecular dynamics (MD) simulations.
• Density functional theory (DFT) calculations.

Main Results:

• Identified a novel vacancy-ordered SrFeO_2+σ phase during SrFeO₃ reduction.
• Observed pathway bifurcation during oxidation, leading to direct conversion or a cascade of intermediates under different temperature conditions.
• MD simulations revealed a crossover in oxygen diffusion mechanisms.
• DFT calculations confirmed that intermediate phases are electronically and magnetically distinct.

Conclusions:

• Nonequilibrium pathway selection can lead to functional states not predicted by equilibrium phase diagrams.
• The identified intermediates are not just structural stepping stones but distinct functional phases.
• This work provides insights into controlling phase transitions for novel material properties.