Isomorphous substitutions of rare earth elements for calcium in synthetic hydroxyapatites |
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Authors: | Ardanova Lyudmyla I Get'man Evgeni I Loboda Stanislav N Prisedsky Vadim V Tkachenko Tatiana V Marchenko Valeriy I Antonovich Valeriy P Chivireva Nataliya A Chebishev Konstantin A Lyashenko Alexandra S |
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Institution: | Department of Chemistry and Geology, Minnesota State University, Mankato, 241 Ford Hall, Mankato, Minnesota 56001, USA. lyudmyla.ardanova@mnsu.edu |
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Abstract: | Polycrystalline hydroxyapatites Ca(10-x)REE(x)(PO(4))(6)(OH)(2-x)O(x) were synthesized and studied by X-ray powder diffraction, infrared absorption, diffuse-reflectance spectroscopy, and thermogravimetry. The solubility limits x(max) of rare earth elements (REE) in Ca hydroxyapatites decreases with an increasing REE atomic number from x(max) = 2.00 for La, Pr, and Nd to x(max) = 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. |
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