Mechanism of Substitution in Carbonated Apatites

Single‐phase AB‐type carbonate apatites were prepared by sintering appropriate mixtures of CaHPO 4 and CaCO 3 at 870°C in a CO 2 atmosphere with a partial water vapor pressure of 5 mm Hg. Chemical and physical analyses indicate that at a constant CO 3 2− /OH − ratio in the hydroxyl sublattice, carbonate substitutes for phosphate on a 1:1 mole basis. For every three PO 4 3− ions substituted, two vacancies in the Ca 2+ sublattice and one in the OH − sublattice are created. The same substitution mechanism seems to apply in pure B‐type carbonate apatite.