Comparison of local structure between Mg/Mn-doped natural and synthetic hydroxyapatites by X-ray absorption spectroscopy

The natural hydroxyapatites were extracted from fish bone. In the extracted process, Mg and Mn were added in hydroxyapatite. In addition, Mg/Mn-doped hydroxyapatites were synthesized by sol-gel combustion method. This study compared local sites of Mg and Mn in natural and synthetic hydroxyapatites. The crystal and local structures were investigated by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) technique, respectively. For Mg-added, the results indicate that Mg2+ for the both natural and synthetic hydroxyapatites, but they form MgO structure and rather substitute on Ca site in CaO structure, respectively. For Mn-added, the results indicate Mn4+ for synthetic HAp and mixture ion of Mn3+ and Mn4+ for natural HAp. The calculated XANES spectra show that Mn is formed to Ca3Mn2O7 structure in Mn-doped synthetic HAp and the mixture phase between CaMn2O4 and Ca3Mn2O7 for natural HAp.