Reinvestigation of the crystal structure of Ca2Ce8(SiO4)6O2 apatite by Rietveld refinement

Ca2Ln8(SiO4)6O2 apatites with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd and Tb crystallize in space group P63/m. The crystal structure of apatite-type Ca2Ce8(SiO4)6O2 [dicalcium octacerium hexakis(silicate) dioxide], which has been synthesized by calcination, was refined from powder X-ray diffraction data using the Rietveld method. A database survey shows that contrary to the previously published Ca2Ce8(SiO4)6O2 structure [Skakle et al. (2000). Powder Diffr. 15, 234–238], the cell volume of the structure reported here is consistent with those of other Ln apatites