Abstract: | The crystal structure of thallium carbonate, Tl2CO3 (C2/m, Z = 4), is stable at least up to 3.56 GPa, as demonstrated by hydrostatic single‐crystal X‐ray diffraction measurements in a diamond anvil cell at room temperature. Our results contradict earlier observations from the literature, which found a structural phase transition for this compound at about 2 GPa. Under atmospheric conditions, all atoms except for one O atom reside on the mirror plane in the high‐pressure structure. The compression mainly affects the part of the structure where the nonbonded electron lone pairs on the Tl+ cations are located. |