Neutron powder diffraction studies of silicon-substituted hydroxyapatite

The incorporation of a small amount of silicon in the hydroxyapatite (HAp) lattice is known to improve the bioactivity of the material. The effect of silicon substitution was studied by comparing samples of pure and 0.4 wt% silicon-substituted HAp prepared by an aqueous precipitation method. High-resolution neutron powder diffraction and Rietveld refinement methods were used to investigate the effect of silicon substitution on the crystal structure parameters of the HAp lattice from room temperature down to 20 K. Small structural changes in the lattice constants, interatomic distances, site occupancies and distortion of the phosphate tetrahedron were found. Modifications of the Fourier transform infrared spectra as well as appearance of new modes were observed in the silicon-substituted sample. Heat treatment and silicon substitution also affected the morphology and crystallinity of this bioapatite.