Manganese in apatites, chemical, ligand-field and electron paramagnetic resonance spectroscopy studies

Abstract

Hydroxapatites precipitated with different amounts of carbonate and Mn²⁺ were studied. Infrared spectra, X-ray diffraction lattice parameters and thermal behaviour indicate that the presence of Mn²⁺ does not have any effect on the formation and properties of the carbonate apatites obtained. Interaction of apatite with a Mn²⁺-containing aqueous solution reveals that the molar uptake of Mn²⁺ by the apatite is higher than the Ca²⁺ released by it. Ligand-field and electron paramagnetic resonance spectroscopy results show that in Mn²⁺-doped Cd₅(PO₄)₃Cl, Mn²⁺ replaces Ca²⁺ in the apatite lattice, but in precipitated carbonate apatite it is in an MnO phase. The conclusion that Mn²⁺ in precipitated carbonate apatites is not incorporated in the apatite crystal is discussed in the light of the size differences between Mn²⁺ and Ca²⁺.