Percolation and Modeling of Proton Conduction in Polymer/Brushite Composites

Composites have been fabricated by compressing polycrystalline brushite mixed with a polymer powder into pellets to study the surface activities and proton mobilities of acid CaHPO4·2H2O phosphates (brushite). The electrochemical properties of such composites are studied using complex impedance spectroscopy analyses. Two types of surface proton migrations have been observed by following the water content of the samples. The various proton migrations through these granular materials and the percolation threshold of these currents are interpreted using various modeling approaches. Three models are used and compared: the effective medium approximation (EMA), a model based on the percolation theory, and a semiempirical microstructural electrical model.