Electrical characterization of hydroxyapatite-based bioceramics

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz–1 MHz at temperatures from room temperature to 1000 °C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 °C. At temperatures below 700 °C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700–1000 °C), bulk ionic conduction was dominant and activation energies were of the order of ∼2 eV, indicating that hydroxyl ions are responsible for conductivity.