CHARACTERIZATION BY TEM OF LOCAL CRYSTALLINE CHANGES DURING IRRADIATION DAMAGE OF HYDROXYAPATITE COMPOUNDS

Local crystalline changes during transmission electron microscopy (TEM ) examination of hydroxyapatite (OHAp) compounds have been revealed by combining electron diffraction analysis and the Moire fringe method. The latter is a sensitive tool for the detection of small crystal vari ations induced by beam irradiation damage in the OHAp structure. TEM o bservations suggest that a hexagonal (P6(3)/m) to monoclinic (with b = 2a) transformation could occur as a possible result of beam-induced s toichiometry changes. Such order-disorder transformations seem to be r elated to very small local crystal lattice rotations as deduced by the changing of the Moire patterns period under the electron beam. (C) 19 95 Academic Press, Inc.