High temperature Jahn-Teller distortion and short-range order in CsCuCl$_3$

Abstract

CsCuCl$_3$, chiral and Jahn-Teller distorted at room temperature, takes a more symmetric structure above 423 K. Describing this 'simpler' high temperature structure is far from simple and has been the subject of many, sometimes contradicting, studies. Here we reinvestigate the high temperature structure of CsCuCl$_3$, its thermal stability, and its effect on room temperature chirality. In situ pair distribution function data from powder neutron diffraction confirms that CsCuCl$_3$ is Jahn-Teller distorted both below and above $T_\mathrm{c}$, and provides a quantitative view of short-range order in the high temperature structure. In situ powder x-ray diffraction shows that CsCuCl$_3$ does not undergo any additional structural changes above 423 K and is congruently melting. In situ single crystal x-ray diffraction experiments reveal that the phase transition induces domains of mixed handedness in originally homochiral crystals. These findings contribute to a better understanding of phase transitions in Jahn-Teller distorted compounds, and highlight the potential use of phase transitions to control chiral domains.