J. Belana et al., BEHAVIOR OF AMORPHOUS POLY(ETHYLENE-TEREPHTHALATE) ANNEALED AT T-LESS-THAN-TG BY THERMALLY STIMULATED CURRENTS, Journal of Materials Science, 28(14), 1993, pp. 3805-3808
Thermally stimulated current (TSC) discharges in open circuit of amorp
hous poly(ethylene terephthalate) (PET) corona-charged electrets show
a heteropolar relaxation at 87-degrees-C, rho1, between alpha and rho
peaks. This relaxation tends to become homopolar when the sample is an
nealed at temperatures below the glass transition temperature. This is
due to the formation of a trapped charge density on the surface of th
e material that originates, during the TSC discharge, a current that c
ounteracts the one that results in rho1. This trapping effect, which i
nitially is null, increases with annealing due to the rise in resistiv
ity. On the other hand, TSC discharges in short-circuited annealed sam
ples result in a heteropolar peak, rho, that corresponds to rho1. The
area of rho increases with the annealing time in a bounded way. This
peak is related to the formation of thermal nuclei (embryos) in the b
ulk of the material that act as heterogeneities. This suggests that rh
o1 is associated with a barrier-type polarization. If the annealed sam
ple is heated to temperatures above the glass transition temperature,
the tendency to the inversion of rho1 vanishes and rho disappears, wh
ereas alpha and rho are modified. This suggests that rho relaxation is
related to a Maxwell-Wagner-Sillars effect.