Superlattice ordering transitions driven by short-range structure in barium calcium carbonates.

Balcite (BaCaCO) is a synthetic analog of rhombohedral carbonate minerals like calcite and dolomite that is disordered on both the cation and anion sublattices. Here, we show that multiple exotic superlattice structures, including a dolomite analog that we call balcomite, can form from balcite at elevated temperatures. The second-order balcite-to-balcomite conversion at temperatures between 150-600 °C is driven by the preference of barium and calcium for different oxygen coordination numbers and facilitated by local carbonate reorientation.