Hydroxyapatite has a unique structure in that it is conductive along the hydroxide channels. OH- ions lie at (1/4/,1/4,1/4) and (3/4/,3/4,3/4) on the c-axis and charge-carrying protons are responsible for the observed conductivities in M10(PO4)6(OH)2. The H+ migration between the electroattractive ion (O2) to give molecular H2O in matrix channels carries charge and the resulting conductivity.
The unit cell consists of two triangular prismatic subcells forming a rhombic prism with vertical sides. There are two horizontal mirror planes at the OH levels of 1/4 and 3/4 of the c-axis. In addition, there is a center of inversion exactly in the center of each vertical face of each subcell.
