Crystal structure of lead hydroxyapatite from powder X-ray diffraction data

The crystal structure of lead hydroxyapatite, Pb-10(PO4)(6)(OH)(2), is refined on powder XRD data using the Rietveld method. The unit cell is hexagonal, a=b=9.866(3) and c=7.426(2) Angstrom, space group P6(3)/m, Z=1 (relative to the specified formula). Results are discussed and compared with previous structures of hydroxyapatite and partially lead-substituted hydroxyapatites. Now that the entire range of lead substitution is covered, it is possible to detect a coherent trend in the distortions of the crystal packing introduced by the different ability of the two metallic crystal sites to accommodate Pb ions.