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Chemistry of Materials 23 (2011) 3072-3085
Unexpected Mechanism of Zn2+ Insertion in Calcium Phosphate Bioceramics
S. Gomes1, J.-M. Nedelec1, Edouard Jallot2, D. Sheptyakov3, G. Renaudin1

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.
1 :  LMI - Laboratoire des Matériaux Inorganiques
2 :  LPC - Laboratoire de Physique Corpusculaire [Clermont-Ferrand]
3 :  Laboratory for Neutron Scattering ETHZ & Paul Scherrer Institut
Sciences du Vivant/Ingénierie biomédicale/Biomatériaux


biomaterials – zinc doping – calcium phosphates – Rietveld refinement – Raman