Percolation and modeling of proton conduction in polymer/brushite composites

Composites have been fabricated by compressing polycrystalline brushite mix ed with a polymer powder into pellets to study the surface activities and p roton mobilities of acid CaHPO4 . 2H(2)O phosphates (brushite), The electro chemical properties of such composites are studied using complex impedance spectroscopy analyses. Two types of surface proton migrations have been obs erved by following the water content of the samples. The various proton mig rations through these granular materials and the percolation threshold of t hese currents are interpreted using various modeling approaches. Three mode ls are used and compared: the effective medium approximation (EMA), a model based on the percolation theory, and a semiempirical microstructural elect rical model. (C) 1998 Academic Press.