Studies by thermally stimulated current (TSC) of hydroxy- and fluoro-carbonated apatites containing sodium ions

Carbonated hydroxyapatites (HAPCO(3)Na) and fluoroapatites (FAPCO(3)Na) containing sodium ions have been precipitated by the hydrothermal method. The effect of carbonate and sodium substituted for phosphate and calcium respectively on the dipolar mobility of the OH- and F- ions located inside the apatitic channels of those samples has been studied by thermally stimulated current (TSC). in both apatites two relaxation modes, around -100 and +50 degrees C, have been observed. In the HAPCO(3)Na sample, the relaxation mode fine structure reveals the existence of two cooperative phenomena with compensation temperatures in the vicinity of the hydroxyapatite monoclinic-hexagonal transition. After preheating of samples at 400 degrees C, the presence of cooperative movements is confirmed by the observation of a compensation phenomenon with a compensation temperature equal to 214 degrees C. An x-ray diffraction study is in agreement with this attribution. As for the FAPCO(3)Na sample, the fine structure of the lower temperature relaxation mode only reveals a compensation phenomenon at 5 degrees C attributed to water molecule reorientations inside apatitic channels.