Thermally Stimulated Currents and Voltages and Dielectric Properties

Abstract

Experimental techniques for charging and observing thermally stimulated currents and voltages (TSC and TSV) in polymers and crystals are described and an outline is given of the theory of the processes. The polymers are corona charged, and trapping takes place near one surface. In an attempt to determine the microscopic nature of the traps, a study is made of a polyolefin series of ten polymers. Charge storage is shown to take place mainly along the chains themselves and through caging between neighboring molecules. In addition, the corona itself may produce changes in the polymers to create primary trapping sites. Charge storage stability is a function of electronegativity of the ions, symmetry along the chains, and packing density. The crystal work consists of a study of impurity‐vacancy (I – V) dipoles in doped alkali halides, such as , Eu++, Yb++, and Ca++. The dipoles are field polarized. Analysis of the thermally stimulated dipolar peaks yields relaxation times, activation energies, and dipole concentrations. Other I – V dipole phenomena that may be studied with these techniques are described. A comparison is made between information obtainable from TSC and the more normal dielectric constant‐loss tangent measurements, and we conclude that TSC is a valuable aid in the characterization of insulators. These studies also yield information on the basic electrical conduction mechanisms in insulators. The paper concludes with suggestions for further work and practical applications.