Dynamic Barriers to Crystallization of Calcium Barium Carbonates

Metastable carbonates play important roles in geochemistry, biomineralization and serve as model systems for nonclassical theories of nucleation growth. Balcite (Ca0.5Ba0.5CO3) is a remarkable carbonate phase that isostructural with high-temperature modification calcite (CaCO3), yet can be synthesized at ambient conditions. Here, we investigate crystallization pathways the Ba–Ca–CO3–H2O system, focus on transformation amorphous calcium barium (ACBC) to balcite subsequent decomposition into equilibrium (CaCO3) witherite (BaCO3) phases. Density functional theory calculations show an unstable solid solution (Ca1–xBaxCO3, R3̅m) range 0.17 < x 0.5, but accessible through ACBC precursor ≲ predict its witherite. We confirm this pathway experimentally found demixing proceed slowly remain incomplete even after 9 months. Nucleation kinetics from was assessed using microfluidic assay, where increasing content led surprising increase rate, despite decreasing thermodynamic driving force. attribute rates dramatically accelerate time changes interfacial structure composition during coarsening precipitate. By carefully quantifying kinetic contributions multistep metastable carbonate, produce insights allow us better interpret formation persistence minerals natural synthetic environments.