Localization of potassium in substituted lead hydroxyapatite:: Pb9.30K0.60(PO4)6(OH)1.20 by X-ray diffraction

An adaptation of the double decomposition method for apatites preparation is tested on lead apatite and applied to the synthesis of lead hydroxyapatite partially potassium substituted. The structure of the sample is carried out by the Rietveld method using powder XRD measurement. The compound crystallizes in the hexagonal system (space group P6(3)/m) with the following cell: a = b = 9.8461(3) Angstrom, c = 7.3591(3) Angstrom. Final agreement factors R-p, R-wp, R-B, and R-F are 0.16, 0.11, 0.037, and 0.031, respectively. Results are discussed and compared with those for Pb-10(PO4)(6)(OH)(2). According to site occupancy factors, potassium prefers to occupy the site 4f (site(I)). Moreover the structure contains vacancies in both lead and hydroxyl sites. A global mechanism of potassium substitution for lead is proposed. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.