Structure Analysis of A-Type Carbonate Apatite by a Single-Crystal X-Ray Diffraction Method

The crystal structure of carbonate apatite was determined by X-ray diffraction analysis with Rw=0.027 using a single crystal grown by a CaCO3 flux method. The chemical formula of the crystal was Ca9.75[(PO4)5.5(CO3)0.5]CO3, in which all the A sites corresponding to OH sites in hydroxyapatite were substituted by CO3 ions. The space group was P (hexagonal) with lattice parameters of a=0.9480(3) nm and c=0.6898(1) nm. The triangular plane of the CO3 ion substituting the A site randomly occupied one of six equivalent sites around the axis parallel to the c-axis; one of three C–O bonds of CO3 lay on the axis. The quantitative relation between CO3 ions in the A (OH) site and B (PO4) site of the present crystal was accounted for via Ca deficiency.