Les hydroxyapatites mixtes de strontium et de cadmium, Cd x Sr ( 1 0 - x ) (PO 4 ) 6 (OH) 2 , ont ete synthetisees par double decomposition en phase aqueuse. Elles ont ete caracterisees par diffraction des rayons X, RMN-MAS 3 1 P et par spectroscopie infrarouge. L'affinement structural sur poudre par les methodes de Rietveld a permis de preciser la limite de la solution solide strontium-cadmium (x=<4), ainsi que la repartition du cadmium dans le reseau apatitique. La faible amplitude de variation de δ i s o ( 3 1 P) entre Sr 1 0 (PO 4 ) 6 (OH) 2 (δ i s o =2,9 ppm) et Cd 1 0 (PO 4 ) 6 (OH) 2 (δ i s o =12,2 ppm) ne permet pas de separer les signaux isotropes associes aux differents environnements de l'ion phosphate dans les apatites mixtes. La substitution progressive de Cd 2 + a Sr 2 + , dans les sites S 1 et S 2 de la maille apatitique, n'entrane pas de distorsion notable du tetraedre PO 4 , ainsi que le revele la faible augmentation de l'anisotropie de deplacement chimique du phosphore-31 lorsque x augmente.
X-ray powder diffraction, solid-state 3 1 P-MAS-NMR and IR spectroscopy of cadmium-strontium mixed hydroxyapatites. Strontium-cadmium hydroxyapatite solid solutions Cd x Sr ( 1 0 - x ) (PO 4 ) 6 (OH) 2 were prepared in aqueous medium. They were characterized by X-ray powder diffraction, 3 1 P-MAS-NMR and IR spectroscopic analyses. The structural refinement, by X-ray powder pattern fitting (Rietveld method), indicates the limits of strontium-cadmium solid solutions (x=<4) and allows us to determine the cadmium repartition in the apatite cell. Through the progressive replacement of Sr 2 + (r=1.32 9) by the smaller cation Cd 2 + (r=1.09 9), all interatomic distances decrease according to the decrease of the cell parameters. However, contrary to what could be expected from the coordinance of the metallic sites S 1 (hexacoordination) and S 2 (heptacoordination) the small cadmium cation does not preferentially occupy the four sites S 1 : it is almost statistically distributed over both sites, with a slight preference for S 2 . The 3 1 P- solid-state-NMR of the pure phases Sr 1 0 (PO 4 ) 6 (OH) 2 and Cd 1 0 (PO 4 ) 6 (OH) 2 reveals a moderate chemical shift anisotropy (~20 ppm) corresponding to slight distortion of the phosphate tetrahedron. This observation holds also for the mixed species where the surrounding of the phosphate anion is expected to change significantly when substituting Cd for Sr. Through the progressive replacement of strontium by cadmium, the isotropic signal moves regularly to high frequency, according to the deshielding observed for Cd 1 0 (PO 4 ) 6 (OH) 2 (δ i s o =12.2 ppm) with respect to Sr 1 0 (PO 4 ) 6 (OH) 2 (δ i s o =2.9 ppm). Moreover the isotropic signal broadens considerably because of unresolved chemical shift distributions in the highly disordered material. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAShydroxyapatite / Rietveld refinement / 3 1 P-MAS-NMR / cadmium / strontium / phosphate