Physicochemical properties and structural refinement of strontium-lead hydroxyapatites

Continuous series of solid solutions of strontium and lead apatite Sr(10-x)Pbx(PO4)(6)(OH)(2) (0 less than or equal to x less than or equal to 10), synthesized in aqueous media have been investigated by X-ray powder-pattern fitting, P-31 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 P-31 MAS NMR spectra at 162 MHz show a unique isotropic signal at delta(iso) between +2.9 (SrHA) and -0.7 ppm (PbHA). From the variation of delta(iso) with the phase composition it appears that P-31 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 T-d symmetry shown by the Rietveld refinement analysis