Tuning Orbital Order in Fluoride Perovskite KFeF3 via high pressure

Oxide-based perovskites have received significant interest through extensive structural and theoretical studies, however the adjacent playground of the fluoride analogues, ABF3 have comparatively attracted far less attention. While previous high resolution PXRD analysis has elucidated orbital order in some of the fluoride perovskites such as NaCrF3, KCrF3, NaCuF3 and KCuF3 exhibiting eg active JT distortions at room temperature, there has been little work exploring cooperative JT distortions associated t2g degeneracies in these systems. Here we propose a high-pressure neutron diffraction experiment on PEARL to probe the interplay between octahedral tilting and orbital ordering in KFeF3, and overlooked member of the ABF3 family that has such a t2g degeneracy. These experiments will shed fundamental insight on the interplay between orbital and tilt degrees of freedom in the fluoride perovskites, helping unlock their potential for use in functional materials in emerging technologies such as battery cathodes and memristive devices.