X-ray powder diffraction and solid-state NMR investigations in cadmium-lead hydroxyapatites

In the proposed experiment, the maximum amount of cadmium substitution in lead hydroxyapatite accounts for about to 30 atom-%. The crystal structures of PbHA at different degrees of cadmium substitution for lead (4.9, 10.0, 22.4 and 29.0% Cd atoms) have been investigated by X-ray powder pattern fitting and P-31 MAS NMR. The site-occupancy factors of metal atoms clearly indicate a preference of cadmium for site 1 of the apatite structure, which is more selective at low cadmium content. A progressive shift of the OH group wards the center of the triangles formed by the site 2 metalshas been observed with increasing cadmium content. The different environments of the phosphate group demonstrated by P-31 NMR spectroscopic data are discussed in relation to structural data.