Jahn–Teller distortion in perovskite KCuF3 under high pressure

Single crystals of KCuF3 have been grown by the solution method. We report neutron diffraction under high pressure up to 8 GPa on a powder sample pulverized from KCuF3 crystals. The type-A spin ordering structure found in KCuF3 can be well-explained based on the orbital ordering resolved from this structural study. In comparison with perovskite oxides, the fluoride exhibits a much reduced bulk modulus. Our results also reveal the change of local structural distortion as a function of pressure; the magnitude of Jahn–Teller distortion at ambient condition is dramatically suppressed under high pressure. Extensive comparison of the pressure dependence of the Jahn–Teller perovskite fluoride with that of analogous perovskite oxides has also been made.

Graphical abstractThe configuration Cu:d9 in the cubic crystal field leads to the Jahn–Teller distortion in the perovskite KCuF3. The figure illustrates a 0 0 1 layer of the perovskite KCuF3 where the 3x2 − r2/3y2 − r2 orbital is occupied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Crystal structure of the perovskite KCuF3 has been studied by neutron powder diffraction under high pressure. ► The structural distortion is compatible to a orbital–lattice interaction instead of the orbital ordering due to the superexchange interaction. ► The long-rang Jahn–Teller distortion in the perovskite KCuF3 remains stable under high pressure to 8 GPa. ► The bulk modulus of KCuF3 is smaller than that in other Jahn–Teller inactive perovskite fluorides.