ELECTROCHEMICAL PROPERTIES OF POLYMER PHOSPHATE COMPOSITES/

To study the surface activities and proton mobilities of CaHPO4.2H(2)O phosphates in powdered states, composites have been fabricated by mix ing polycrystalline phosphates with polymer or CaO powders. The electr ochemical properties of such composites, compressed into pellets, are studied using complex impedance spectroscopy analyses. We measure the critical volume fraction corresponding to the percolation of ionic cur rents through the solid composites; The influence of adsorbed water mo lecules on electric properties is clearly shown. Using home made Volta battery devices, the percolation threshold is accurately determined: a very low value of 12 vol.% for the volume fraction of phosphate or 2 5 vol.% taking into account the cavities, is observed. This low value is interpreted. A model using the effective medium approximation is us ed to describe some of the experimental results.