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Wenhao Sun1 Gerbrand Ceder1

1, Lawrence Berkeley National Labs, Berkeley, California, United States

Vaterite is a transient metastable polymorph of calcium carbonate that often appears during the multistage crystallization of CaCO3. Nucleation of vaterite prior to the equilibrium phase calcite should, according to classical nucleation theory, be facilitated by a lower surface energy of vaterite than calcite. We perform a thorough density functional theory investigation of calcite and vaterite surface energies, and find, contrary to expectations, that vaterite unequivocally has the higher surface energy of the two phases. Here, we present a novel mechanism to rationalize the preferential nucleation of vaterite. Because the vaterite crystal structure is composed of alternating Ca2+/CO32- planes in the [001] direction, nanoparticles of vaterite possess a permanent electrostatic dipole moment. We show that nuclei of vaterite can be stabilized relative to calcite under electric fields that are consistent with charge inhomogeneities on mineral surfaces, in biogenic macromolecules, and in aqueous electrolyte solutions. The role of electric fields in nucleating the polar polymorph of CaCO3 can be more generally leveraged to synthesize metastable polar phases of other materials, potentially opening the door to materials with novel or superior functionality.

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