Tetrahedra Rotational and Displacive Disorder in the Scheelite-Type Oxide CsReO₄

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Scheelite-type metal oxides are vital functional materials with diverse applications.
• Understanding structure-property relationships, especially at local scales, is crucial for material engineering.
• Cesium rhenium oxide (CsReO4) presents a unique pseudo-scheelite structure.

Purpose of the Study:

• To investigate the structural behavior of CsReO4 under varying conditions.
• To explore the relationship between average and local structures in CsReO4.
• To understand how A-site cation properties influence structural disorder and material properties.

Main Methods:

• Synchrotron X-ray diffraction (XRD) to study the average crystal structure.
• X-ray pair distribution function (PDF) analysis to probe local atomic arrangements.
• Temperature-dependent structural analysis.

Main Results:

• CsReO4 undergoes a phase transition from orthorhombic (Pnma) to tetragonal (I41/a) symmetry at approximately 440 K.
• Local structural analysis reveals lattice strain and ReO4 tetrahedral rotations above 440 K, inconsistent with average structure symmetry.
• A discrepancy exists between long-range average structure and short-range local structure.

Conclusions:

• The A-site cation's bonding and ionic radius significantly influence structural disorder.
• This disorder is observable across different length scales, impacting material properties.
• Detailed structural insights are essential for optimizing functional metal oxides.