Charles M. Huggins

Dielectric Properties of Some Powdered Organic Semiconductors

The use of electrical conductivity measurements to characterize the charge density and/or mobility parameters of a material is discussed. The common practice of using simple, pressed electrodes with dc measurements is felt to be grossly inferior to four‐probe techniques. Even this refinement, however, is subject to considerable error for powdered samples. Many workers have used fairly simple ac techniques to eliminate interparticle contact resistances in organic semiconductors; this approach is shown to have been misapplied. It is possible, however, to measure what appears to be a specific conductivity (independent of packing pressure or filling factor) by more elaborate ac analysis. Measurements of the effective parallel resistance and capacitance are given for anthracene (powder and single‐crystal), metal‐free β‐phthalocyanine, and a β‐carotene tri‐iodide complex for a frequency range of 0.05 cps to 300 Mc/sec.

Self‐Diffusion in Linear Dimethylsiloxanes

The pressure and temperature dependences of the self‐diffusion coefficients of the linear dimethylsiloxanes, containing from two to nine silicon atoms have been determined by the NMR spin‐echo technique. Activation energies and volumes are presented as derived quantities; the constant‐volume activation energy is estimated from these data. Extensive comparisons between the diffusion properties of the dimethylsiloxanes and equivalent hydrocarbons are made. From these comparisons, it is concluded that diffusion in siloxanes is controlled to a much larger extent by chain configurational effects. This concept is formalized by expressing the chain‐size effects in an entropy of activation model.

Chapter IV: Conduction phenomena in dielectric solids

One of the prerogatives of the authors of any review is the choice of emphasis on those subjects in which the authors are particularly interested. The material covered here reflects, to some extent, just such a preference. The sheer quantity of literature published during the year 1964 which could be included under this general title precludes any completely general coverage in a reasonable-sized review. Hence, a selection was based upon a supposition on the interests of the readers of this volume. On this basis, the strongest interest was centered on materials generally considered as dielectrics and on theory most applicable to dielectric materials. The metals, as well as some other materials exhibiting metallic-like behavior, were in general not included. Likewise, no coverage was extended to the so-called wide-band semiconductors such as silicon and germanium on the assumption that adequate coverage of this subject is a separate work to be found in other sources. The intermetallic semiconductors were excluded on the same principle.