Showing papers on "Charge transfer insulators published in 1988"
TL;DR: In this paper, surface charge measurements on alumina and polymer insulators were carried out after stressing them with DC voltages in a high vacuum, and the order of magnitude of surface charge density was found to be the same for materials with widely varying secondary-emission yields.
Abstract: Surface charge measurements on alumina and polymer insulators were carried out after stressing them with DC voltages in a high vacuum. The order of magnitude of surface charge density was found to be the same for materials with supposedly widely varying secondary-emission yields. Surface coatings on alumina insulators reduced charge accumulation because of increased surface conductivity and/or reduced secondary-emission yield, which led to significant improvement in voltage hold-off for alumina ceramics. Removing the cathode triple junction from the main body of the cylindrical insulator, reducing the X-ray activity in the gap, or relieving the stress at the critical junction did not significantly alter the surface charge characteristics of cylindrical insulators. Wet hydrogen firing of plain alumina reduced the voltage hold-off by 25% without altering the surface charge density. It is postulated that the charging of insulators in bridged vacuum gaps with DC stresses is due to internal secondary emission produced by ionization of the lattice in the surface layer of the insulating material, by primary electrons injected at the cathode triple junction. This mechanism of charge production differs from the current models where charging is believed to occur due to electrons hopping along the surface/vacuum interface. >
78 citations
TL;DR: In this article, the authors describe a novel technique for investigating the motion of free charge in insulators, which involves measurements of the charge transfer in a series of contacts with a (preferably liquid) metal and, simultaneously, the mean distance of the free charge from the insulator surface.
Abstract: The authors describe a novel technique for investigating the motion of free charge in insulators. It involves measurements of the charge transfer in a series of contacts with a (preferably liquid) metal and, simultaneously, the mean distance of the charge from the insulator surface. The technique can detect charge migration over very small distances and it provides a powerful means of elucidating mechanisms of conduction; there is no possibility of confusing free-charge motion with polarisation changes due to e.g. dipole orientation. Their experiments on polymers reinforce previous suggestions that the polymers contain both permanent traps and 'shallow' traps which retain charge for a relatively short time. They suggest, however that this distinction may reflect different degrees of isolation of the electron traps in a relatively loose and mobile network of polymer molecules, rather than differences in their energy.
11 citations
12 Sep 1988
TL;DR: In this paper, the role of the internal electric field in low-temperature electron hopping in an impurity band is examined, taking into account the formation of correlated structures due to electron-electron interactions.
Abstract: Electronic transport processes that take place in insulators are examined in two different temperature regimes. At high temperatures, field-assisted thermal ionization is considered and previous theories are reexamined on the basis of a recently proposed model that includes the role of the internal electric field. As a low-temperature transport mechanism, electron hopping in an impurity band is examined, taking into account the formation of correlated structures due to electron-electron interactions. The theoretical analysis is compared with the experimental electrical conductivity results obtained in CdF/sub 2/-doped crystals over a wide range of applied electric fields and temperatures. >