paper

Structural studies on $A_{2}$ ReCl $_{6}$ ( $A$ =K, Rb, Cs): absence of Jahn-Teller distortion

arXiv:2602.08665 · doi:10.1103/jhcn-vj32

Abstract

K $_{2}$ ReCl $_{6}$ belongs to the antifluorite family and exhibits a sequence of structural transitions above the onset of magnetic order at $T_{N}$ = 12 K. Because of its 5d3 electronic configuration in an octahedral coordination, the ground state is a pure spin state without orbital degeneracy within the LS coupling scheme, but it can become Jahn-Teller active in the strong spin-orbit coupling limit described by the $j j$ coupling [S. Streltsov and D. I. Khomskii, Phys. Rev. X 10, 031043 (2020)]. While the structural transitions in K $_{2}$ ReCl $_{6}$ are understood in terms of octahedral rotation and tilting, the possible impact of a Jahn-Teller distortion remains an open issue. We report on comprehensive crystalstructure studies by means of powder neutron and single-crystal x-ray diffraction on K $_{2}$ ReCl $_{6}$ and on K $_{2}$ SnCl $_{6}$ . The latter material is used as a reference, because it exhibits the same sequence of structural transitions as K $_{2}$ ReCl $_{6}$ , but possesses a filled 4d shell ruling out a Jahn-Teller distortion. While the ReCl $_{6}$ octahedron in K $_{2}$ ReCl $_{6}$ presents sizable distortions at intermediate temperatures, there is no such distortion persisting to low temperatures excluding a sizable Jahn-Teller effect. Studies on polycrystalline samples of Rb $_{2}$ ReCl $_{6}$ and Cs $_{2}$ ReCl $_{6}$ , in which the structural transitions are suppressed due to the larger alkaline ionic radius, also do not find any indications for a Jahn-Teller distortion.

15 pages, 11 figures

Structural studies on A2​ReCl6​ (A=K, Rb, Cs): absence of Jahn-Teller distortion

Abstract

Structural studies on $A_{2}$ ReCl $_{6}$ ( $A$ =K, Rb, Cs): absence of Jahn-Teller distortion