Dielectric properties of stoichiometric and defect-induced hydroxyapatite.

Dehydrated hydroxyapatite (HAp), OH- ion-defect induced hydroxyapatite, was prepared for dielectric measurements. We evaluated the dielectric properties of HAp in 100-500 °C, and found dielectric relaxations of two kinds. At lower temperature, relaxation that was attributed to the reorientations of OH- ions was observed, where the relaxation strengths were influenced strongly by the OH- concentrations. The activation energy of the OH- reorientation, which was unaffected by the OH- concentrations, was ascertained as 0.62-0.63 eV. However, in a higher temperature range, relaxations that had larger relaxation strength were observed and were regarded as originating from the displacement of OH- ions and O2- ions. The activation energies of the larger relaxation, which were affected by the OH- concentrations, were ascertained as 0.73 eV and 0.81 eV. Those values are comparable to the activation energy of proton conduction, implying that the proton conduction in HAp starts at a low temperature. [ABSTRACT FROM AUTHOR]