HOT Article: New model for disorder in vaterite

Vaterite is one of the three crystalline polymorphs of calcium carbonate, and plays a significant role in biomineralisation, either as an intermediate formed from amorphous calcium carbonate prior to transformation to aragonite or calcite, or can be utilized by organisms in its own right.

Recently there have been several key advances in our understanding the formation of calcium carbonate, and owing to its great importance not only in biomineralization the lack of a proper understanding of the solid-state structure of vaterite is certainly a considerable deficit. Despite its significance, there has been considerable debate regarding the nature of the structure of this material. While vaterite is known to exhibit disorder, several ordered structures are used as models to understand its crystal chemistry. In this HOT Article, Demichelis et al. have used ab initio calculations to show that the two most widely used structural models are actually transition states, rather than being stable, and that the third proposed literature model is too high in energy to be viable. Several new distorted structures for vaterite are proposed that are very close in energy and able to interchange, thereby creating a mechanism to explain the observed disorder. The final nature of the disorder may ultimately depend on the kinetics of the transformation from a precursor phase, as postulated for the ikaite to vaterite conversion.

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A new structural model for disorder in vaterite from first-principles calculations
Raffaella Demichelis, Paolo Raiteri, Julian D. Gale and Roberto Dovesi
CrystEngComm, 2011, Advance Article

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