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 i s tested on lead apatite and applied to the synthesis of lead hydroxyapatit e partially potassium substituted. The structure of the sample is carried o ut by the Rietveld method using powder XRD measurement. The compound crysta llizes in the hexagonal system (space group P6(3)/m) with the following cel l: a = b = 9.8461(3) Angstrom, c = 7.3591(3) Angstrom. Final agreement fact ors 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). Ac cording to site occupancy factors, potassium prefers to occupy the site 4f (site(I)). Moreover the structure contains vacancies in both lead and hydro xyl sites. A global mechanism of potassium substitution for lead is propose d. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights re served.