Syntheses, crystal structures, and comparisons of rare-earth oxyapatites Ca(2) RE (8)(SiO(4))(6)O(2) (RE = La, Nd, Sm, Eu, or Yb) and NaLa(9)(SiO(4))(6)O(2)

Six different rare-earth oxyapatites, including Ca(2) RE (8)(SiO(4))(6)O(2) (RE = La, Nd, Sm, Eu, or Yb) and NaLa(9)(SiO(4))(6)O(2), were synthesized using solution-based processes followed by cold pressing and sinter­ing. 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 hexa­gonal space group P6(3)/m and showed similar unit-cell parameters. The isolated [SiO(4)](4−) tetra­hedra in each crystal are linked by the cations at the 4f and 6h sites occupied by RE (3+) and Ca(2+) in Ca(2) RE (8)(SiO(4))(6)O(2) or La(3+) and Na(+) in NaLa(9)(SiO(4))(6)O(2). The lattice parameters, cell volumes, and densities of the synthesized oxyapatites fit well to the trendlines calculated from literature values.