Isomorphous Substitutions of Rare Earth Elements for Calcium in Synthetic Hydroxyapatites
Chemistry and Geology
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.
Lyudmyla I. Ardanova, Evgeni I. Get’man, Stanislav N. Loboda, Vadim V. Prisedsky, Tatiana V. Tkachenko, Valeriy I. Marchenko, Valeriy P. Antonovich, Nataliya A. Chivireva, Konstantin A. Chebishev, and Alexandra S. Lyashenko. (2010). Isomorphous Substitutions of Rare Earth Elements for Calcium in Synthetic Hydroxyapatites. Inorganic Chemistry, 49 (22), 10687-10693.
Publisher's Copyright and Source
Copyright © 2010 American Chemical Society. Article published by American Chemical Society in Inorganic Chemistry, volume 49, issue number 22 (2010), pages 10687-10693. Available online on October 19, 2010: http://doi.org/10.1021/ic1015127.