Structure of vanadate in calcium phosphate and vanadate apatite solid solutions

Abstract

Polycrystalline solid solutions of phosphate and vanadate calcium apatites were synthesized and studied by XRD, XPS, 31P and 51V NMR, FTIR and UV spectroscopies. Homogeneous distributions of vanadium within the solid and the surface were obtained. While 51V NMR spectra suggest an axial symmetry of the vanadate group, FTIR spectra indicate distortion from essentially C3v symmetry in solid solutions with low vanadium content to Cs for pure vanadate apatite, in agreement with the site symmetry group of phosphate in hydroxyapatite. Refinements of XRD pattern of vanadate apatite by Rietveld method confirm the Cs point group attribution. Three vanadium oxygen bond lengths were found around 168 pm and one close to 174 pm, suggesting that the Cs point group could be generated by a small distortion from C3v symmetry. Analysis of UV spectra confirms that distortion from Td symmetry increases with vanadium content and suggests some contraction of the vanadate ion in the apatite lattice.