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