Electrical conductivity and electron-spin resonance in oxidatively stabilized polyacrylonitrile subjected to elevated temperature

Abstract

The development of electrical conductivity in oxidized polyacrylonitrile (PAN) fiber as a function of heat-treatment temperature has been studied for heat-treatment temperatures in the range 710–950 K. By means of a study of conductivity versus measurement temperature, it is shown that PAN heat treated in vacuum in this temperature range is a semiconductor. The room-temperature conductivity is dominated by the contribution of impurities. The activation energy for the formation of the impurities that contribute to the conductivity is 88 kcal/mole. Electron-spin resonance (ESR) measurements have also been made on these fibers. Studies of the variation of the ESR absorption intensity with temperature reveal that the ESR signal can be analyzed in terms of two components: localized spin centers and charge carriers. The charge-carrier component of the ESR signal is interpreted as being due to the formation of metallic conduction pathways in the polymer. Both the electrical conductivity and the ESR absorption intensity decrease when the samples are aged in air.