The effect of the silicon incorporation on the hydroxylapatite structure.: A neutron diffraction study

Nominal stoichiometric hydroxylapatite, Ca-10(PO4)(6)(OH)(2) and silicon-substituted HA, containing 0.9 wt% in silicon, were prepared by the ceramic method. The samples were analyzed by elemental chemical analysis, Fourier transformed infrared spectroscopy (FTIR) and the structural study was carried out by Rietveld analysis combining powder X-ray (XRD) and neutron diffraction (ND). The refinements of the occupancies at the 4e Wyckoff position shows that the OH-/O2- ratio is higher when SiO44- substitutes PO43-. The observation of the Fourier maps points out that also the HPO42- formation from PO43- is also higher when Si is included in the HA structure. For the first time, the atomic coordinates for the H atoms of HPO42- anions are provided. (C) 2004 Elsevier SAS. All fights reserved.