Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Grain boundaries (GBs) significantly influence material properties, including ionic conductivity.
• Understanding ionic diffusion mechanisms in pyrochlores is crucial for applications like solid oxide fuel cells and batteries.
• Cation disorder can dramatically alter ion transport pathways in complex oxides.

Purpose of the Study:

• To investigate the impact of grain boundaries on oxygen diffusion in pyrochlores.
• To elucidate the role of GB type, chemistry, and cation disorder on ionic transport.
• To explore the transition from 2D to 3D diffusion mechanisms.

Main Methods:

• Molecular dynamics (MD) simulations were employed.
• Simulations analyzed oxygen diffusion across various pyrochlore compositions and disorder levels.
• The concentration and mobility of charge carriers at GBs and in the bulk were quantified.

Main Results:

• Grain boundaries enhance oxygen transport in ordered and low-disorder pyrochlores due to higher carrier concentration and mobility.
• In ordered systems, diffusion is predominantly 2D and localized at GBs.
• With increasing cation disorder, bulk diffusion becomes significant, leading to a transition from 2D/GB-dominated to 3D/bulk-dominated oxygen diffusivity.

Conclusions:

• A transition in oxygen diffusivity from 2D/GB-dominated to 3D/bulk-dominated occurs with increasing cation disorder in pyrochlores.
• Internal interfaces like GBs can be leveraged to enhance ionic conductivity in nanostructured complex oxides.
• These findings offer insights for designing advanced materials with tailored ionic transport properties.