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 diffract ion analysis with R-w = 0.027 using a single crystal grown by a CaCO3 flux method. The chemical formula of the crystal was Ca-9.75[(PO4)(5.5)(CO3)(0.5 )]CO3, in which all the A sites corresponding to OH sites in hydroxyapatite were substituted by CO, ions, The space group was P (6) over bar (hexagona l) with lattice parameters of a = 0.9480(3) nm and c = 0.6898(1) nm, The tr iangular plane of the CO3 ion substituting the (6) over bar site randomly o ccupied one of six equivalent sites around the a axis parallel to the c-axi s; one of three C-O bonds of CO3 lay on the (6) over bar axis. The quantita tive relation between CO3 ions in the A (OH) site and B (PO4) site of the p resent crystal was accounted for via Ca deficiency. (C) 2000 Academic Press .