Magnesium- and fluoride-co-substituted hydroxyapatites (Ca9Mg(PO4)6(OH)2-yFy, where 0≤y≤2, have been synthesized by the hydrothermal method. The X-ray diffraction showed that all the powders were single-phased. The sintering behavior of powders was studied by dilatometry from 25 to 1200°C, and the sintered samples were investigated by using the XRD and scanning electron microscopy. During heating, there was a decomposition of the apatite due to the presence of Mg. The nature of the formed products was closely related to the fluorine content. For the compositions rich in fluorine, the end of the shrinkage was interrupted by the formation of a liquid phase thereby inducing the crystallization of needle like-crystals through a dissolution-diffusion-reprecipitation process.
S. Nsar, E. Ben Salem, K. Bouzouita
Apatite; Sintering; Thermal behavior
Pages: 191-200
The investigated compound Ag1.60Na1.40Al2(AsO4)3 is isostructural to Na3M2(AsO4)3 (M : Al, Ga, Fe) ones. The structure determined by single crystal X-ray diffraction is refined in the space group R-3c until the final agreement factors R=0.022 and wR(F2)=0.053 for 619 reflections with I < 2σ(I). It consists of Al4O18 clusters connected by AsO4 tetrahedra leading to a three-dimensional anionic framework with interconnected cavities where the Na+ and Ag+ cations accommodate. These cations are statistically distributed on several independent positions. The obtained structural result is confirmed by the Bond Valence Sum model (BVS) and the Charge Distribution method (CHARDI). Ionic conductivity measurements by complex impedance spectroscopy (CIS) performed on a powder pellet showed a conductivity of 5.14.10-6 S.cm-1 at 302°C and the title compound is then less conductive than the isostructural sodium phase. A conduction pathway simulation of the monovalent cations, based on the BVS model is proposed. Correlations to crystal data are discussed.
N. Fakhar Bourguiba, A. Guesmi, N. Ouerfelli, D. Mazza, M.F. Zid, A. Driss
Structural study, Ionic conductivity, BVS simulation
Pages: 201-211