31 P and 1 H powder ENDOR study of ozonide radicals in carbonated apatites, synthesized from aqueous solutions

An O 3 − defect in Na+ CO 3 2− containing apatite powder has been investigated with ENDOR after X-irradiation. The powder, synthesized by a hydrolysis of octo-calciumphosphate (OCP) and Na2CO3 was dried at 25°C until constant weight was reached. At low temperatures, both31P and1H ENDOR spectra were recorded for different settings of the magnetic field (i.e., when the magnetic field is swept through the EPR O 3 − spectrum). The ENDOR powder spectra were thoroughly analyzed using computer simulations based on the “orientation selection principle”. Interactions with two types of protons and two types of31P nuclei could be resolved. In this way, a detailed model could be established for the O 3 − ion in the hydroxyapatite lattice. The defect is located between two successive vacant hydroxyl sites. The axis connecting the two outer oxygen atoms (g y-axis) of the O 3 − ion is found to be along the hexagonalc-axis of the lattice. The twofold axis of the defect ion (g z-axis) is parallel to theb-axis of the lattice.