Oxygen Migration Pathways in Layered LnBaCo₂O_6-δ (Ln = La - Y) Perovskites

Area of Science:

• Materials Science
• Solid-State Chemistry
• Catalysis

Background:

• Layered LnBaCo2O6-δ perovskites are crucial mixed ionic-electronic conductors.
• These materials exhibit excellent catalytic activity for oxygen evolution and reduction reactions.
• Structural complexity, especially oxygen vacancy ordering near room temperature, influences their properties.

Purpose of the Study:

• To elucidate the structural features governing ionic migration in layered LnBaCo2O6-δ perovskites.
• To utilize bond valence site energy (BVSE) calculations to understand ion transport mechanisms.
• To identify optimal compositions for enhanced ionic conductivity and catalytic performance.

Main Methods:

• Employing bond valence site energy (BVSE) calculations.
• Analyzing the impact of different lanthanide (Ln) elements (Sm-Tb, Dy, Y) on perovskite structure.
• Investigating oxygen vacancy ordering and its effect on migration pathways.

Main Results:

• BVSE calculations identified key structural determinants for facile ionic migration.
• 1D vacancy ordering (Ln = Sm-Tb) can be beneficial at low temperatures by creating new, lower-barrier pathways.
• 2D vacancy ordering (Ln = Dy, Y) hinders ionic transport; the parent layered structure shows lower migration barriers.
• An expanded ab plane, Ba support, and small Ln size are critical for low migration barriers.
• Ln = Y exhibits the most favorable structure for ionic transport, but is limited by low-temperature 2D ordering and moderate stability.

Conclusions:

• The study clarifies the relationship between structure, oxygen vacancy ordering, and ionic transport in LnBaCo2O6-δ perovskites.
• Ln = Y is predicted to be the optimal composition for ionic conductivity, though practical application requires addressing ordering and stability.
• Findings provide a pathway for designing improved mixed ionic-electronic conductors for catalytic applications, including oxygen cycling.