Syntheses, crystal structures, and comparisons of rare-earth oxyapatites Ca (SiO)O ( = La, Nd, Sm, Eu, or Yb) and NaLa(SiO)O.

Six different rare-earth oxyapatites, including Ca (SiO)O ( = La, Nd, Sm, Eu, or Yb) and NaLa(SiO)O, were synthesized using solution-based processes followed by cold pressing and sinter-ing. The crystal structures of the synthesized oxyapatites were determined from powder X-ray diffraction (P-XRD) and their chemistries verified with electron probe microanalysis (EPMA). All the oxyapatites were isostructural within the hexa-gonal space group 6/ and showed similar unit-cell parameters. The isolated [SiO] tetra-hedra in each crystal are linked by the cations at the 4 and 6 sites occupied by and Ca in Ca (SiO)O or La and Na in NaLa(SiO)O. The lattice parameters, cell volumes, and densities of the synthesized oxyapatites fit well to the trendlines calculated from literature values.