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Unexpected Mechanism of Zn2+ Insertion in Calcium Phosphate Bioceramics

Abstract : Rietveld analysis on X-ray powder diffraction patterns recorded from Zn-doped, Zn/Sr, and Zn/Mg codoped biphasic calcium phosphate (BCP) samples has been used to locate Zn2+ cations in both hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) phases heat-treated at 1100 °C. Zn atoms occupy interstitial sites in HAp (Wyckoff site 2b), leading to an insertion solid solution of general composition Ca10Znx(PO4)6O2x(OH)2-2x. Replacement of hydroxyl by O2- anions with formation of linear O-Zn-O entities should be considered to preserve the electroneutrality of the material. Contrary to HAp case, Zn atoms substitute calcium atoms in β-TCP leading to a substitution solid solution of general composition Ca3-xZnx(PO4)2. Micro-Raman spectroscopy and neutron diffraction have confirmed these insertion/substitution mechanisms. The different mechanisms of zinc incorporation should be considered to stabilize the desired calcium phosphate phase which are managed by the Ca/P and (Ca+Zn)/P ratios. Furthermore, discussion of biological properties of Zn-doped calcium phosphate ceramics should take into account the true insertion mechanism as critically discussed here.
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Submitted on : Monday, July 11, 2011 - 3:43:18 PM
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S. Gomes, Jean-Marie Nedelec, Edouard Jallot, D. Sheptyakov, G. Renaudin. Unexpected Mechanism of Zn2+ Insertion in Calcium Phosphate Bioceramics. Chemistry of Materials, American Chemical Society, 2011, 23, pp.3072-3085. ⟨10.1021/cm200537v⟩. ⟨in2p3-00607861⟩



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