PNNL

Abstract

Six different rare-earth oxyapatites including Ca2RE8(SiO4)6O2 (RE = La, Nd, Sm, Eu, Yb) and NaLa9(SiO4)6O2 were synthesized using solution-based processes followed by heat treatments. The crystal structures of the synthesized oxyapatites were solved from X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA). All the oxyapatites were isostructural with the hexagonal space group P63/m and showed similar unit cell parameters. The isolated [SiO4]4- tetrahedra in each crystal are linked by the cations at 4f and 6h sites occupied by RE3+ and Ca2+ in Ca2RE8(SiO4)6O2 or La3+ and Na+ in NaLa9(SiO4)6O2. The lattice parameters, cell volumes, and densities of the synthesized oxyapatites fit well to the trendlines calculated from literature values. The compositions of crystals were verified with EPMA measurements.