In this paper the Sessler's treatment (ST) for radiation induced conductivity in open circuit, in which the material nuder electron beam irradiation is supposed to acquire a conductivity and to accumulate mobile as well as trapped charges, is applied to the case of irradiation under a voltage. We show that ST is an approximation of a more complex treatment where the generation-recombination process is explicitly considered while allowing a single species to move. ST leads to good results for the back electrode current and for charge profiles if the electric field is so directed as to drive the mobile charges into the sample Bulk In general, trapping causes the agreement to be worse. An implicit finite difference scheme was employed in the numerical integration to ensure greater accuracy.
This paper presents an approximate universality displayed by thermally stimulated depolarization currents ruled by stretched exponential relaxations when properly re-scaled. A visually perfect universality occurs especially when the energy and the heating rate are varied. It becomes somewhat poorer when the frequency factor or the stretched exponent changes. Empirical relations between the half widths and other pertinent parameters are given.
TSDC measurements were carried out with samples of 60:40 and 70:30 molar ratios of VDFI'l'rFE copolymers. The 60(VDF):40(TrFE) copolymer presented a current peak around 90 'C, associated with its ferroelectric-to-paraelectric (F-P) transition.The 70:30 copolymer also presented the F-P peak and, in addition, another peak a t n lower temperature, identified as a phase transition between two ferroelectric phases. A model combining fast and slow polarization processes were developed t o explain the TSDC curves. The fast process was connected to t h e phase transition, and the slow one was composed by the thermal depolarization of dipolar units of the &phase crystallites and the variation of the pyroelectric current.
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