Structure of vanadate in calcium phosphate and vanadate apatite solid solutions

Polycrystalline solid solutions of phosphate and vanadate calcium apatites were synthesized and studied by XRD, XPS, P-31 and V-51 NMR, FTIR and UV sp ectroscopies. Homogeneous distributions of vanadium within the solid and th e surface were obtained. While V-51 NMR spectra suggest an axial symmetry o f the vanadate group, FTIR spectra indicate distortion from essentially C-3 v symmetry in solid solutions with low vanadium content to C-s for pure van adate apatite, in agreement with the site symmetry group of phosphate in hy droxyapatite. Refinements of XRD pattern of vanadate apatite by Rietveld me thod confirm the C-s point group attribution. Three vanadium oxygen bond le ngths were found around 168 pm and one close to 174 pm, suggesting that the C-s point group could be generated by a small distortion from C-3v symmetr y. Analysis of UV spectra confirms that distortion from T-d symmetry increa ses with vanadium content and suggests some contraction of the vanadate ion in the apatite lattice.