| |
[摘要]：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 Zn(2+) cations in both hydroxyapatite (HAp) and beta-tricalcium phosphate (beta-TCP) phases heat-treated at 1100 degrees C. Zn atoms occupy interstitial sites in HAp (Wyckoff site 2b), leading to an insertion solid solution of general composition Ca(10)Zn(x)(PO(4))(6)O(2x)(OH)(2-2x). Replacement of hydroxyl by O(2-) 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 beta-TCP leading to a substitution solid solution of general composition Ca(3-x)Zn(x)-(PO(4))(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. |
|
