Atomic‐Scale {101¯0} Interfacial Structure in Hydroxyapatite Determined by High‐Resolution Transmission Electron Microscopy

The atomic structure of {101¯0} interfaces in sintered hydroxyapatite (HAp) was characterized using high‐resolution electron microscopy (HRTEM). When subjected to electron beam radiation parallel to the [0001] zone axis, a characteristic damage of HAp occurred. The damage was identified by hexagonally shaped regions surrounded with {101¯0} planes, in which the crystalline phase was thinned and amorphized. HRTEM study at the crystalline‐amorphous interfaces revealed that the HAp crystal structure was terminated by a plane crossing the hydroxyl columns on which Ca (Ca2 site) and PO 4 tetrahedra were placed. The grain boundaries parallel to the {101¯0} planes were also examined and the structure was identical to that observed in the crystalline‐amorphous interface. The interface structure observed in the crystalline‐amorphous interfaces and grain boundaries is probably a stable atomic arrangement of HAp {101¯0} surfaces with a low surface energy.