Anomalous thermally stimulated currents and space charge in poly(vinyl pyrrolidone)

To study the mechanisms of charge production and storage in poly(vinyl pyrrolidone) (PVP), short circuit thermally stimulated currents (TSCs) in solution-grown PVP depolarized at 30, 50 and 80 °C with 25, 50 and 100 kV cm−1 have been analysed in the temperature range 30–200 °C. By employing TSC measurements with a conventional ‘contact electrode’ two kinds of charges have been observed. An anomalous TSC flowing in the same direction as the charging current was observed for PVP thermoelectrets poled at 50 and 80 °C with 50 and 100 kV cm−1. The TSCs for samples poled at different temperatures (30, 50 and 80 °C) with 25 kV cm−1 have been found to be normal in the sense that the discharge current flows in the direction opposite to that of the charging current. The TSC thermograms have been found to be characterized by two peaks located at 60–70 °C and 160–170 °C. Various characteristics of thermograms have been explained in terms of the existence of heterocharge due to dipolar orientation and ionic homocharge drift, together with the injection of charge carriers from electrodes and their subsequent localization in surface and bulk traps.