ELECTRON-STRUCTURE OF A GRAIN-BOUNDARY AND A CRYSTAL OF CALCIUM-PHOSPHATE BIOCERAMIC (HYDROXYAPATITE)

The electron structure of the typical calcium phosphate ceramic, hydro xyapatite (OHAP), is investigated by the use of the tight-binding recu rsion method. The local density of states, partial density of states, structural energy and charge transfer are calculated, as well as the i nteratomic energy between atoms and bond order integral. Some physical and chemical properties of OHAP are discussed. The calculated results show that both the OH group and the PO4 group can be regarded as indi vidual structure units in OHAP owing to strong interaction between ato ms. Meanwhile, the atomic structure of a grain boundary is determined on the basis of the near-coincidence site lattice model with considera tion of the bond length in the crystal and the lattice distortion. The electron structure and energy of a Sigma = 7 grain boundary are calcu lated. The results show that a grain boundary with a slight lattice mi sfit has a lower energy.