Calcite has the ability to host large amounts of intracrystalline inclusions, a phenomenon that is known to be the case in biominerals and has been demonstrated in bioinspired synthetic systems. In this study, barium ion is focused on as the inclusion. Highly substituted Ba-calcite possesses disordered carbonate orientations, characteristic of (Formula presented.) symmetry. It is shown that calcite experiences an order–disorder transition, in which the carbonate groups undergo progressive loss of their rotational order with increasing amounts of incorporated Ba, and reach complete rotational disorder for a critical amount of Ba. This transition is characterized and a theoretical model justifying the influence of Ba is proposed. Moreover, the disordered (Formula presented.) Ba-substituted calcite has been previously identified as a high-temperature phase or as a highly metastable room-temperature phase. Those descriptions are challenged by successfully synthesizing it under slow-rate conditions and by studying its thermal behavior, and it is concluded that the fully disordered Ba-calcite is stable, whereas the transitional, partially disordered Ba-calcite phase is metastable.
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- phase transition