The ac complex conductivity σ*(f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1–100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of σ*(f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites.

A series of measurements carried out with the point-to-plane symmetry has shown that positive corona confirms the Townsend relation while for the negative corona this happens only at large point-to-plane distances (greater than 1.5 cm). In this case, the ratio of the prefactors in Townsend relation, for the same geometry, approaches the expected constant (the ratio of the mobilities) at larger distances, around 6 cm. For distances below 1.5 cm, the square root of the current is linear with the voltage, with an intercept of ∼1.4 kV. The results are interpreted as giving evidence of an electronic component at small distances, as suggested by Sigmond. The characteristics change to Townsend at higher distances when the electronic component becomes small as compared with the ionic one.

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This paper reports results of measurements of radiation-induced conductivity of Teflon @ (Teflon is a registered trademark ofthe E. J. du Pont de Nemours and Co.). FEP (polyfluorethylene propylene) foils irradiated by x rays at atmospheric pressure. The current induced by irradiation of the poled dielectric at exposure rates of the order of 10 2 Rls, initially increases with time for 10-20 s, reaches a maximum, and subsequently decreases. After an irradiation time of about 1 h, a steady-state value is attained which is of the order of 25% of the maximum current. Measurements are reported of the dependence of the current amplitudes on exposure rate, of the delayed component of induced conductivity, and of the behavior of samples which had been irradiated in short-circuit before poling. Radiation-induced polarization effects or space-charge formation could not be detected. The behavior of the current-time curves is interpreted in terms of a theory of unipolar (hole) conduction.PACS numbers: 36.20. -r, 61.80.Cb 3.75 X let V Icm.