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Role of Impurities in the Kinetic Persistence of Amorphous Calcium Carbonate: A Nanoscopic Dynamics View

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journal contribution
posted on 07.07.2018, 00:00 by Ayumi Koishi, Alejandro Fernandez-Martinez, Beatrice Ruta, Monica Jimenez-Ruiz, Roberta Poloni, Devis di Tommaso, Federico Zontone, Glenn A. Waychunas, German Montes-Hernandez
Amorphous calcium carbonate is found in the early stages of biomineral formation. Its moldability and its kinetic persistence against crystallization make it of potential interest to the development of biomimetic materials. The presence of water and of inorganic impurities such as Mg2+ has been reported to increase its kinetic stability. Yet, the precise mechanisms of stabilization as well as the link between structural dynamics and crystallization kinetics are still missing. Here, we report the vibrational and diffusive dynamics of water and other atomic constituents in a series of Mg2+-doped solid amorphous calcium carbonates revealed using coherent X-ray and incoherent neutron scattering. This unique combination of techniques presents a novel view on the nanoscopic dynamic behavior of these amorphous materials: the presence of Mg2+ results in a higher frequency of structural rearrangements within the material. However, this increased dynamic behavior does not translate into a higher crystallization kinetics because of a concomitant stiffening of the water hydrogen bond network.