Syntheses and Crystal Structures of Rare-Earth Oxyapatites Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm)

• DOI: 10.1007/s10870-020-00857-y
• Publication Date: 2020-08-28T11:03:49Z
• Authors: Saehwa Chong; Brian J. Riley; Emily T. Nienhuis; Dongjin Lee; John S. McCloy
• Keywords: Space group; Powder Diffraction

Four different rare-earth oxyapatites of Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying, calcination, and high-temperature sintering in air. X-ray powder diffraction and Raman spectroscopy were performed on the synthesized oxyapatites. The RE oxyapatites crystallize in the hexagonal space group P63/m with similar unit cell parameters, increasing linearly with larger RE cations. The unit cell volumes increase linearly whereas the densities decrease nonlinearly with larger RE cations. Raman spectra showed intense bands of the symmetric bending and stretching modes of SiO4 at ~ 400 and 860 cm−1 regions, respectively. The bands generally shifted to higher frequencies with smaller RE cations in the structures. Rare-earth oxyapatites Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm) crystallize in the hexagonal space group P63/m, and their unit cell parameters increase linearly with larger RE cations.