High‐Resolution Electron Microscopy and Convergent‐Beam Electron Diffraction of Sintered Undoped Hydroxyapatite

Abstract

Transmission electron microscopy (TEM) was used to characterize the microstructure of sintered undoped hydroxyapatite (OHAp). Conventional TEM observations were accom‐panied by high‐resolution electron microscopy (HREM) and convergent‐beam electron diffraction (CBED) studies. CBED analysis enabled the determination of the space group of the OHAp, P63/m. Densification of the material was performed by pressureless sintering at 1250°C for 30 min. The undoped sample was comprised of apatite as the only crystalline phase, in addition to a small volume fraction (4%) of closed porosity. In general, the observed microstructure was homogeneous and consisted of equiaxed apatite grains with an average grain diameter of }1–2μm. No indication of a residual amorphous phase, which may have formed during sintering, was observed at multigrain junctions. HREM studies on grain boundaries also revealed that no intergranular glass film was present along two‐grain junctions, indicating that densification proceeded without a liquid phase. A slightly disordered region at the interfaces was observed, suggesting an extended grain‐boundary structure.