Study of structure of calcium phosphate materials by means of electron spin resonance

Structure of γ-irradiated calcium phosphates synthesized in different conditions was studied by means of ESR. It has been shown that amorphous and nanocrystalline calcium phosphates have qualitatively different ESR spectra. The new paramagnetic center in hydroxyapatite (HA) has been found. It consists of four protons of water molecules located in the parallelogram vertexes and the free electron formed in HA by γ-irradiation. This center is thermally stable up to 300 °C, when the water molecules release from the HA crystal lattice.

► We study structure of calcium phosphates by ESR.
► We have found that ACP samples have short-range order in an atom arrangement.
► We offer a new model of paramagnetic center in hydroxyapatite.