Isomorphous Substitutions of Rare Earth Elements for Calcium in Synthetic Hydroxyapatites

Document Type

Article

Publication Date

2010

Abstract

Polycrystalline hydroxyapatites Ca10−xREEx(PO4)6(OH)2−xOx were synthesized and studied by X-ray powder diffraction, infrared absorption, diffuse-reflectance spectroscopy, and thermogravimetry. The solubility limits xmax of rare earth elements (REE) in Ca hydroxyapatites decreases with an increasing REE atomic number from xmax = 2.00 for La, Pr, and Nd to xmax = 0.20 for Yb at 1100 °C. Refinements of X-ray diffraction patterns by the Rietveld method show that REE atoms substitute for Ca preferentially at the Ca(2) sites of the apatite structure. The substitution decreases the Ca(2)−O(4) atomic distances in the calcium coordination polyhedra and increases the Ca(2)−O(1,2,3) distances. This observation shows that interatomic distances depend not only on radii of the ions involved in the substitution but also on their charges.

Department

Chemistry and Geology

Publication Title

Inorganic Chemistry

DOI

10.1021/ic1015127

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