The presence of structural defects in modified hydroxyapatite samples was studied. The behaviors of samples having various compositions were compared. Structural alterations were produced by heat treatment and high-energy milling. Electron paramagnetic resonance spectroscopy was used to identify the presence of structural defects. Samples were analyzed at room temperature, and the electron paramagnetic resonance signals which were observed at g = 1.999 were attributed to O vacancies in the apatite structure. The determination of the vacancy concentration in each sample was related to characteristic parameters of the signal, and to the experimental conditions. X-ray diffraction and scanning electron microscopy were used as additional characterization techniques. The production and concentration of vacancies were related to modifications which were introduced during processing. The results were also related to the chemical composition, particle size and crystallinity of the samples.

Structural Analysis of Modified Hydroxyapatite Powders. M.A.Fanovich, M.S.Castro, J.M.Porto Lopez: Materials Research Bulletin, 2001, 36[3-4], 487-96