Synthesis, structural model and vibrational spectroscopy of lutetium tricalcium phosphate Ca9Lu(PO4)7

Lutetium β-tricalcium phosphate Ca9Lu(PO4)7was synthesized by solid-state reaction at 1200 °C, and investigated by means of a combination of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. SEM morphological analysis reveals the presence of sub spherical and prismatic micro crystalline aggregates, while EDS semi-quantitative analysis confirms the nominal Lu/Ca composition. The unit cell and the space group were determined by X-ray powder diffraction data showing that the compound crystallizes in the rhombohedral R3cwhitlockite-type structure, with unit cell constants a = b = 1.04164(1) nm, c = 3.7302(1) nm and cell volume V = 3.5051(1) nm3. The investigation was completed with the structural refinement by the Rietveld method, and discussion of the distribution of Lu within cationic sites according to the results of the Rietveld refinement. The FTIR and Raman spectra, correlated to isostructural rare earth phosphates from literature, show slight band shifts of the phosphate modes correlated to the evolving size of the rare earth elements.