1. Unlocking the mysterious polytypic features within vaterite CaCO3.
- Author
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San, Xingyuan, Hu, Junwei, Chen, Mingyi, Niu, Haiyang, Smeets, Paul J. M., Malliakas, Christos D., Deng, Jie, Koo, Kunmo, dos Reis, Roberto, Dravid, Vinayak P., and Hu, Xiaobing
- Subjects
VATERITE ,BIOSPHERE ,CALCIUM carbonate ,CALCITE ,PHASE transitions ,MOLECULAR dynamics ,TRANSMISSION electron microscopy ,MACHINE learning - Abstract
Calcium carbonate (CaCO
3 ), the most abundant biogenic mineral on earth, plays a crucial role in various fields such as hydrosphere, biosphere, and climate regulation. Of the four polymorphs, calcite, aragonite, vaterite, and amorphous CaCO3 , vaterite is the most enigmatic one due to an ongoing debate regarding its structure that has persisted for nearly a century. In this work, based on systematic transmission electron microscopy characterizations, crystallographic analysis and machine learning aided molecular dynamics simulations with ab initio accuracy, we reveal that vaterite can be regarded as a polytypic structure. The basic phase has a monoclinic lattice possessing pseudohexagonal symmetry. Direct imaging and atomic-scale simulations provide evidence that a single grain of vaterite can contain three orientation variants. Additionally, we find that vaterite undergoes a second-order phase transition with a critical point of ~190 K. These atomic scale insights provide a comprehensive understanding of the structure of vaterite and offer advanced perspectives on the biomineralization process of calcium carbonate. The structure of vaterite has been debated for a century. Combining systematic TEM characterisations, crystallographic analysis, and machine learning aided molecular dynamics simulations, the authors unlock the structural mystery in vaterite. [ABSTRACT FROM AUTHOR]- Published
- 2023
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