X-ray Powder Diffraction and Solid-State NMR Investigations in Cadmium−Lead Hydroxyapatites

Abstract

In the proposed experiment, the maximum amount of cadmium substitution in lead hydroxyapatite accounts for about 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 31P 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 towards the center of the triangles formed by the site 2 metals has been observed with increasing cadmium content. The different environments of the phosphate group demonstrated by 31P NMR spectroscopic data are discussed in relation to structural data.