These bands are significantly more intense in the nanostructured materials at (q(H2O)Na, q(Sr)) = (0.5, 1.0) than in the well-crystallized hydroxyapatite made of microrods at (q(H2O)K, q(Sr)) = (2.8, 1.0), which suggests that Mn(IV) is found mostly in the amorphous component detected by TEM (Figure ). This speciation between the nanocrystalline and amorphous domains can be ascribed to the poor stability of the amorphous phase and possibly to the rapid precipitation of this amorphous material.