Vaterite Microdisc Mesocrystals Exposing the (001) Facet Formed via Transformation from Proto-Vaterite Amorphous Calcium Carbonate

Vaterite is the thermodynamically least stable phase of the three anhydrous calcium carbonate phases. So far there have been no reports showing the synthesis of pure phase vaterite single crystals exposing the (001) facet without the aid of any additive. Herein, single crystalline vaterite microdiscs exposing the (001) facet with high surface energy have been successfully obtained for the first time in isopropanol without the presence of any additives. The process progresses via amorphous calcium carbonate (ACC) precursors. To study this, Ca K-edge extended X-ray absorption fine structure characterization was performed under cryo-condition. The results indicate that the ACC precursor has a short-range order structure similar to that of vaterite, previously named "proto-vaterite ACC". Molecular dynamic (MD) simulations indicate that the binding energy between the (001) facet of vaterite and isopropanol is much higher than those of other facets of vaterite with isopropanol, which might be the reason for the formation of vaterite microdiscs exposing the (001) facet. In summary, the thermodynamically less stable phase vaterite microdiscs exposing the (001) facet were realized for the first time without the presence of any additive, and its formation mechanism was investigated in detail based on the experimental results and MD simulations.