Electrical properties of semiconductor/conductor composites: Polypyrrole-coated tungsten microparticles

Abstract

Tungsten microparticles were coated with globular or nanotubular polypyrrole in situ during the oxidation of pyrrole in aqueous medium with ammonium peroxydisulfate or iron(III) chloride, respectively. The resulting core–shell composites with various contents of tungsten were obtained as powders composed of metal particles embedded in a semiconducting polymer matrix. The coating of tungsten with polypyrrole was analysed by FTIR and Raman spectroscopies. The resistivity of composite powders was determined by the four-point van der Pauw method as a function of pressure applied up to 10 MPa. The degree of compression was also recorded and its relation to electrical properties is discussed on the basis of the percolation concept. The electrical properties of composites are afforded by polypyrrole matrix and they are independent of tungsten content. As the conducting tungsten particles are separated by polypyrrole shells, they cannot produce conducting pathways and behave similarly as a nonconducting filler.