Dielectric and piezoelectric properties of hydroxyapatite-BaTiO3 composites

This letter describes the relationships between the composition and the dielectric and piezoelectric properties of hydroxyapatite-barium titanate composites for polarized bone substitutes. The ac conductivity and permittivity were characterized from $0.1\mathrm{Hz}\text{to}1\mathrm{MHz}$ , along with measurements of the $d_{33}$ piezoelectric charge coefficient. The addition of $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ led to an increase in permittivity and ac conductivity of the material. The increase in both properties was attributed to the presence of the high permittivity ferroelectric phase. The $d_{33}$ and $g_{33}$ coefficients decreased rapidly as hydroxyapatite was introduced into $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ material. Composites below 80% by volume of $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ exhibited no net piezoelectric effect.