Electrical conduction in fluoropolymer films

Isothermal charging, discharging and transport currents in fluoropolymer films are measured in the temperature range of 50 to 200°C at electric fields to 40 MV/m. The currents are measured as a function of time elapsed after the application of steady state voltages in the range of 1 to 10⁴ s. Charging currents increase with time to 10³ s, depending upon the electric field and temperature of the polymer. For longer duration the currents decrease with time. Discharging currents decrease monotonically with time and the discharge current-time characteristics are dissimilar to charging current-time characteristics. Transport currents which are derived by subtracting the discharging currents from charging currents are shown to arise due to Schottky emission assisted by the electric field. At shorter time intervals (<10³ s), it is suggested that the electric field at the cathode increases due to heterocharges and gives rise to currents increasing with time, while for longer times, gradual filling of the traps results in a decrease of the current. Low frequency dielectric loss factors are evaluated from the discharging current measurements