Identification of an apparent peak by use of the final thermally stimulated discharge current technique

The final thermally stimulated discharge current (FTSDC) technique can be used to analyze charge trapping and transport in insulating materials. The experimental conditions can be selected so that the FTSDC is mainly determined by the space charge detrapping. Measurements of the FTSDC in a wide temperature range including the local (secondary) β relaxation and the non-local (primary) α relaxation, for different polymers, demonstrate the existence of an apparent peak. The shift of peak temperature T_m with respect to the charging temperature T_p is analyzed. The interval T_m - T_p decreases from about 25 K to zero, as T_p approaches the glass transition T_g. T_m - T_p is lower for materials of lower conductivity. The peak width at the half maximum intensity decreases as T_p increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and detrapping processes are affected by the strong thermal motion.