Possible Substitution Mechanisms for Sodium and Carbonate in Calciumhydroxyapatite

On the basis of sterical and electrostatical arguments, it is deduced that the stoichiometry of Na+‐ and CO32‐‐containing calciumhydroxyapatite can be accounted for by 6 substitution mechanisms magnified image where Vxstands for a vacancy in the X‐sublattice. It is shown that every mechanism proposed in the literature up to now can be related to these fundamental mechanisms, or to a linear combination of some of them, in this respect, these 6 mechanisms offer an indispensable basis for a systematic derivation of the mechanisms that account for the Na+‐ and CO32‐‐incorporation in some particular apatites. The contributions of each of these mechanisms should be estimated on the basis of a thorough chemical as well as physical analysis of the samples.