Giant Lattice Expansion through Structural Frustration Release in a Dense Oxide

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Large lattice responses in dense inorganic oxides are usually caused by structural phase transitions or redox processes.
• These processes typically alter crystal symmetry or composition, limiting their applications.

Purpose of the Study:

• To identify a novel mechanism for giant lattice responses in dense oxides.
• To investigate the role of structural frustration and cation redistribution in driving these responses.
• To explore potential applications of such materials in advanced technologies.

Main Methods:

• High-pressure quenching of Barium Ruthenium Oxide (Ba ₄ Ru ₃ O ₁₂ ).
• High-resolution synchrotron X-ray diffraction to analyze structural changes.
• Thermogravimetric analysis, transport, and magnetic measurements to rule out other mechanisms.
• First-principles calculations to model cation behavior and energy landscapes.

Main Results:

• Ba ₄ Ru ₃ O ₁₂ exhibited an irreversible 4.4% volumetric expansion between 450 and 650 K.
• The expansion occurred while maintaining R3̅m symmetry and oxygen stoichiometry.
• Cooperative redistribution of Ruthenium (Ru) cations within RuO ₆ trimers was identified as the driving force.
• This cation redistribution was linked to changes in lattice volume, independent of electronic or magnetic transitions.

Conclusions:

• Symmetry-preserving cation redistribution is a distinct mechanism for giant lattice responses in dense oxides.
• Metastable, structurally frustrated configurations offer a route to large, reversible structural changes.
• This finding opens new avenues for designing materials with tunable properties for various applications.