High resolution electron microscopic study of a Ga-containing carbonate apatite

Gallium-containing carbonate apatite was prepared by a precipitation method and studied by high resolution electron microscopy (HREM). HREM micrographs were observed for individual crystals along the 〈2111〉, 〈5140〉, 〈3031〉, 〈3034〉, 〈2110〉, 〈2112〉, 〈2241〉, 〈3030〉 and 〈0001〉 axes. The observed images of these crystals were closely related to the computer-simulated image of the unit cell of hydroxyapatite. About 40% of the crystals showed structural defects, dislocations and grain boundaries. Dislocations have mixed edge and screw character. The structural defects observed apparently demonstrate the disturbing effect Ga has, under the conditions of this work, on the crystallization process of these crystals, probably due to the size and charge difference between Ga and Ca. Consequently, the noticed clinical observations concerning bone resorption decrease may be linked to pure solubility effects since the presence of dislocations induced higher reactivity of the crystals.