Dielectric properties of hydroxyapatite based ceramics

J.P. Gittings (1), C.R.Bowen (1), I.G.Turner (1), A.C.E.Dent, F.R.Baxter (1), (2) and J.B. Chaudhuri (2)

(1) Department of Mechanical Engineering, University of Bath,BATH, BA2 7AY.
(2) Department of Chemical Engineering, University of Bath,BATH, BA2 7AY.

Abstract

This paper studies the ac conductivity and permittivity of hydroxyapatite based ceramics (HA) at temperatures from room temperature to 1000ºC. HA 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 surface adsorbed water on conductivity and permittivity. Surface bound water was thought to contribute to conductivity for both dense and porous materials at temperature below 200ºC. At temperatures below 700ºC the permittivity and ac conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000ºC), bulk ionic conduction was dominant and activation energies are in the range of ~2eV, indicating that hydroxyl ions are responsible for conductivity.