Tetrahedral Displacive Disorder in the Scheelite-Type Oxide RbReO 4 .

Oxides exhibiting the scheelite-type structure are an important class of functional materials with notable applications in photocatalysis, luminescence, and ionic conductivity. Like all materials, understanding their atomic structure is fundamental to engineering their physical properties. This study outlines a detailed structural investigation of the scheelite-type oxide RbReO 4 , which exhibits a rare long-range phase transition from I 4 1 / a to I 4 1 / amd upon heating. Additionally, in the long-range I 4 1 / a model, the Re-O tetrahedral distance undergoes significant contraction upon warming. Recent studies of other scheelite oxides have attributed this apparent contraction to incoherent local-scale tetrahedral rotations. In this study, we use X-ray pair distribution function analysis to show that RbReO 4 undergoes a unique symmetry-lowering process on the local scale, which involves incoherent tetrahedral displacements. The rare I 4 1 / a to I 4 1 / amd long-range phase transition was found to occur via a change from static to dynamic disorder on the local scale, which is due to the combination of the size of the A -site cation and lattice expansion. This demonstrates how careful manipulation of the ionic radius of the A -site in the scheelite structure can be used to induce local-scale disorder, which has valuable implications for tailoring the physical properties of related materials.