Physicochemical Properties and Structural Refinement of Strontium‐Lead Hydroxyapatites

Abstract

Continuous series of solid solutions of strontium and lead apatite Sr(10−x)Pbx(PO4)6(OH)2 (0 ⩽ x ⩽ 10), synthesized in aqueous media have been investigated by X-ray powder-pattern fitting, 31P MAS NMR and IR spectroscopy. The lattice dimensions and the IR frequencies of the solid solutions vary linearly with the atom% of lead. The results of the Rietveld analysis indicated a clear preference of lead for the M(2) site of the apatitic structure, so that in the samples with low Pb content it is almost exclusively found in the M(2) site. 31P MAS NMR spectra at 162 MHz show a unique isotropic signal at δiso between +2.9 (SrHA) and −0.7 ppm (PbHA). From the variation of δiso with the phase composition it appears that 31P shielding in these mixed apatites is essentially governed by the nature of the metal in the M(1) site. The qualitative variation of the chemical shift anisotropy of the PO4 group agrees with the deviation from ideal Td symmetry shown by the Rietveld refinement analysis. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)