Symmetry Breaking in K2IrCL6 and related halides

The present proposal seeks to establish the origin of the observed anomalies in the temperature dependence of the M-X bond distances in some cubic antifluorite-type A2MX6 (A = alkali metals; M = Metal; X = halides) hexahalides. We propose that this originates from disordered tilts of the MX6 octahedra that locally breaks the cubic symmetry that remains intact over larger length scales. The persistence of such disorder to very low temperatures is believed to be a consequence of very weak interactions between neighbouring MX6 octahedra. We will achieve this through variable temperature total scattering studies of three compounds: K2IrCl6, K2PtCl6, and K2SnCl6