September 2, 2020
Journal Article

Shape-preserving amorphous-to-crystalline transformation of CaCO3 revealed by in situ TEM

Zhaoming Liu
Zhisen Zhang
Zheming Wang
Biao Jin
Jinhui Tao
James De Yoreo
Ruikang Tang

Abstract

Organisms use inorganic ions and macromolecules to regulate crystallization from amorphous- precursors, endowing natural biominerals with complex morphologies and enhanced properties. The mechanisms by which modifiers enable these shape preserving transformations are poorly understood. We used in situ liquid-phase transmission electron microscopy to follow the evolution from amorphous calcium carbonate to calcite in the presence of additives. A combination of contrast analysis and infrared spectroscopy shows that Mg ions, which are widely present in seawater and biological fluids, alter the transformation pathway in a concentration-dependent manner. The ions bring excess (structural) water into the amorphous bulk so that a direct transformation is triggered by dehydration in the absence of morphological changes. Molecular dynamics simulations suggest Mg-incorporated water induces structural fluctuations, allowing transformation without the need to nucleate a separate crystal. Thus, the obtained calcite retains the original morphology of the amorphous state, biomimetically achieving the morphological control of crystals seen in biominerals

Revised: September 2, 2020 | Published: February 18, 2020

Citation

Liu Z., Z. Zhang, Z. Wang, B. Jin, D. Li, J. Tao, and R. Tang, et al. 2020. "Shape-preserving amorphous-to-crystalline transformation of CaCO3 revealed by in situ TEM." Proceedings of the National Academy of Sciences of the United States of America 117, no. 7:3397-3404. PNNL-SA-155767. doi:10.1073/pnas.1914813117