INFLUENCE OF FECL3 DOPANT ON THE ELECTRICAL-CONDUCTIVITY OF PYROLYZEDAROMATIC POLYMERS

FeCl3 is used as a dopant of organic semiconductors which have polycon jugated structures (e.g. polyacetylene, polyphenylene), as well as for the intercalation of graphite. Semiconducting polymers can be also sy nthesized by the pyrolytic conversion of organic polymers. The influen ce of FeCl3 as a dopant for pyrolysed aromatic polymers at different p yrolysis temperatures up to 1000 degrees C on their electrical conduct ivity, sigma, has been investigated. In the materials poly-p-phenylene , o, m, p-polyphenylenes, novolac resin cured with hexamethylenetetram ine, biomass of olive stones, lignin Kraft isolated from this biomass, three regions can be distinguished. The electrical conductivity is lo w up to 500 degrees C, between 500 and 700 degrees C it increases grea tly, and above 700 degrees C it increases at a lower rate. For o, m, p -polyphenylenes, these regions (especially the first and the second) c annot be distinguished. Similar curves are generally obtained after do ping of the pyrolysed materials. The ratio of the electrical conductiv ity of doped, sigma to undoped, sigma(0), pyrolysed materials increase s mainly between 500 and 700 degrees C with the exception of o, m, p-p olyphenylenes, where the electrical conductivity decreases at all of t he pyrolysis temperatures. The electrical conductivity of the material s is more strongly influenced by heating than by doping. The results a re interpreted based on the structure of the materials using X-ray dif fractograms, weight losses during the pyrolysis, and taking into consi deration the reactions occurring during pyrolysis. FeCl3 is an effecti ve dopant for organic semiconductors affected by charge transfer, but a less effective dopant for pyrolysed polymers and which do not lead t o intercalation because of the low order and extension of the carbon l ayer formed in comparison to graphite.