Isomorphous substitutions of rare earth elements for calcium in synthetic hydroxyapatites.
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.
Ardanova
Lyudmyla I
LI
Department of Chemistry and Geology, Minnesota State University, Mankato, 241 Ford Hall, Mankato, Minnesota 56001, USA. lyudmyla.ardanova@mnsu.edu
Get'man
Evgeni I
EI
Loboda
Stanislav N
SN
Prisedsky
Vadim V
VV
Tkachenko
Tatiana V
TV
Marchenko
Valeriy I
VI
Antonovich
Valeriy P
VP
Chivireva
Nataliya A
NA
Chebishev
Konstantin A
KA
Lyashenko
Alexandra S
AS