Dielectric properties of stoichiometric and defect-induced hydroxyapatite

Abstract

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.