High-Resolution Transmission Electron Microscopy Observation of Thermal Decomposition Process of Ca-Deficient Hydroxyapatite

Ca-deficient hydroxyapatite whiskers which were prepared by hydrolysis of α-tricalcium phosphate were annealed in air. Planar defects were often observed in the specimen annealed at 600-800 °C. The defects traversing in the whisker in parallel with the (100) plane of the hydroxyapatite crystal expanded into unidentified layered phase with increasing annealing temperature. Since the phase disappeared in the specimen annealed at 900 °C, it is considered as a metastable phase appearing in the thermal decomposition process. The results of EDS microanalysis and IR analysis suggest the metastable phase is a Ca-rich phase.