Ionic substitutions in biphasic hydroxyapatite and β-tricalcium phosphate mixtures:: Structural analysis by rietveld refinement

The structural information on the influence of ionic additions in biphasic (hydroxyapatite (HAP) and beta-tricalciumphosphate (beta-TCP)) mixtures ranging from single ionic substitutions to combined ionic substitutions of most of the essential ions embedded in biological apatite was analyzed through the Rietveld refinement technique. The results have proved that the determined quantitative phase composition of HAP and beta-TCP in biphasic mixtures was dependent on the initial calcium (Ca) deficiency of the precursor powders precipitated from the different molar concentrations used in the synthesis. The substitution of cations (Na+, Mg2+, and K+) improved the stabilization of the beta-TCP structure whereas anions (F- and Cl-) were found incorporated at the OH- site of the HAP phase. Rietveld analysis of X-ray powder diffraction data from the present study proved to be a powerful technique to describe the position and occupancy of certain ions like Mg2+ and Cl- in the biphasic mixtures. However, it has also shown limitations in tracking back other ions like Na+, K+, and F-, which require the use of other complementary characterization methods.