Probing disorder in isometric pyrochlore and related complex oxides

Area of Science:

• Materials Science
• Crystallography
• Solid-State Chemistry

Background:

• Understanding unconventional ordering and its energetic role is crucial for materials with complex structures.
• Isometric pyrochlore compounds (A2B2O7) can transform into disordered fluorite structures (A, B)4O7 under extreme conditions.
• The influence of local ordering on the energy landscape of these transformations remains poorly understood.

Discussion:

• Neutron total scattering reveals that disordered fluorite structures, whether intrinsic or radiation-induced, contain local orthorhombic structural units.
• These units are arranged by a pseudo-translational symmetry, leading to coexistence of orthorhombic and isometric arrays at varying length scales.
• A similar mechanism is observed for inversion in isometric spinel structures.

Key Insights:

• Disordered fluorite structures are characterized by a repeating local orthorhombic unit and pseudo-translational symmetry.
• The study elucidates the coexistence of different structural symmetries (orthorhombic and isometric) across multiple length scales.
• The findings provide a novel framework for comprehending order-to-disorder transformations in crystalline materials.

Outlook:

• This research offers a new basis for understanding order-to-disorder transformations in materials.
• The insights are relevant for optimizing materials for applications such as plutonium immobilization, fast ion conduction, and thermal barrier coatings.
• Further investigation into the energetic landscape and predictive modeling of such transformations is warranted.