Electronic conductivity mechanisms

The resulting materials have approximately equal ionic and electronic contributions to the total conductivity at doping levels between Ce0.8Pro.202-s and Ce0.75Pr0.25O2-s. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+. 

An example of a layer structure mixed conductor is provided by the cathode material L CoC used in lithium batteries. In this solid the ionic conductivity component is due to the migration of Li+ ions between sheets of electronically conducting C0O2. The production of a successful mixed conductor by doping can be illustrated by the oxide Cei-jPxx02- Reduction of this solid produces oxygen vacancies and Pr3+ ions. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+, and the ionic conductivity is essentially vacancy diffusion of O2- ions. 

Different electron conduction mechanisms of a MOS have been proposed including neck controlled (bulk trap and surface trap limited) conduction, and barrier controlled (barrier limited) conduction. A better understanding of the conduction mechanisms will be helpful in developing more effective MOS based sensors. 

Once a note of caution is expressed, novel DNA-based molecular design and architectures have, however, reached levels where the emerging supramolecular structures can perhaps become robust to different electronically working environments. Redox- and fluorophor-labeled molecules offer steps towards device-like function where both structural organization and, as noted, additional sophisticated electronic function can be added to the DNA-based molecules. " " " New electronic conductivity mechanisms based on hopping via a chain of well-defined redox probes bound in the DNA-backbone were noted above." Such... 

History-free, reproducible, transient currents are reported in as-received and Na doped PI films between 150 and 330°C. From a calculation of the total charge transported, purely ionic mechanisms can be ruled out, and an electronic conduction mechanism must be invoked. The electronic conduction is, however, modulated by the presence mobile ionic impurities. The current and total charge transported vary in proportion to the amount of Na ions in the film. Thus an ion/electron interaction in PI is postulated. 

Since these first reports, Iwahara and other investigators have studied the conductivities (both ionic and electronic), conduction mechanism, deuterium isotope effect, and thermodynamic stability of these materials. The motivation for most of this work derives from the desire to utilize these materials for high temperature, hydrogen-fiieled solid oxide fuel cells. In a reverse operation mode, if metal or metal oxide electrodes are deposited onto a dense pellet of this material and heated to temperature T, the application of an electric potential to the electrodes will cause a hydrogen partial pressure difference across the pellet according to the Nemst equation ... 

OCM catalytic properties of R-based mixed oxide ceramic membranes appeared to be determined by the synthesis method, oxygen permeation from one side to the other, surface composition, and the electronic conduction mechanism. 

These radical cations are termed polarons based on the physical description of similar states in solid state physics. Their relevance to the electronic conduction mechanism in these films has been discussed elsewhere [86]. 

Sharma et al. reported a novel and cost-effective fabrication of the CNT/ PPy nanocomposite on the poly(4-styrenesulfonic acid) (PSS)-dispersed MWNTs [79]. PSS not only stabilized the MWNT suspension but also provided charged groups to facilitate an ordered and uniform growth of pseudo-capacitive materials around the MWNTs through electrostatic attractions. The in situ oxidation of Py with KMnO yielded molecular-level dispersion of the MnO in PPy matrix that improved the electronic conductivity, mechanical stability, and pseudo-capacitance. The MWNT-PSS/PPy MnOj ternary nanocomposite exhibited a high SC of 268 F/g at 5 mV/s and only 7% faded in the specific capacity at 100 mV/s and 10% faded in the same after 5000 CV cycles (Figure 8.9). 

Proteins in the body liquids may be considered as a colloidal electrolyte solute in a water solvent. Contact with water is the natural state of a protein. In more or less dry form, a protein powder loses some of its electrolytic character it loses the charged double layer on the surface and behaves electrically very differently from protein with water. Such materials may well be mixed conductors—electronic in the dry state and ionic with water content. Keratin is a more or less dry protein found in the natural state of no longer living biological materials such as hair, nails, and the stratum corneum. The water content of such materials is dependent on the relative humidity of the ambient air. The question of ionic or electronic conductivity in proteins is important, and an electronic conduction mechanism must be considered in many cases. 

Optical techniques have been used to clarify the electronic conduction mechanism and the electrochemical film conversion process [142-144]. Redondo et al. [143] employed ellipsometry [144] to optically probe films grown on platinum electrodes in hydrochloric acid solutions. The optical information may be used to draw conclusions on film density variations as a function of polymerization conditions and film thickness. More important, by potential cycling, films could be examined while undergoing conversions from the reduced (insulating) forms to the oxidized (conducting) forms. Redox reactions carried out on polyaniline-coated electrodes suggest that polyaniline conducts solely in its oxidized emeraldine salt state. 

High-temperature polyimides are used as an excellent electrical insulator in microelectronic devices. This is due to the fact that the CTCs formed in PI films are classified into a category of weak CT complex, and therefore, have practically no contribution to the charge-separated structure at the ground state. Fainshtein et al. [116] showed that the increases in pressured and temperature cause a decrease in the electrical resistance in the dark for Pis derived from a fixed diamine (ODA) with PMDA, BTDA, and 3,3 4,4 -diphenylsulphonetetracarboxylic dianhydride. These results were explained in terms of an electron conductance mechanism based on interchain CTC formation. 

Lor an intrinsic semiconducting oxide where the electronic conductivity mechanism can be described in terms of a large polaron mechanism, the temperature dependence of aei can be written by combination of Eqs. 6.47 and 6.52... 

Lor other oxides it has been suggested that the interactions between the electronic defects and the surrounding lattice can be relatively strong and more localised. If the dimension of the polaron is smaller than the lattice parameter, it is called a small polaron or localised polaron, and the corresponding electronic conduction mechanism is called a small polaron mechanism. 

However, at high temperatures (for oxides above roughly 500 °C) the band theory provides an inadequate description of the electronic conduction mechanism. The energy levels of electrons and electron holes do not form bands, but are locahsed on specific atoms of the crystal stmcture (valence defects). It is... 

Owen, A. E. Electronic Conduction Mechanisms in Glasses, The Glass Industry, part I, pp. 637-642, November, 1967 part II, pp. 695-699, December, 1967. 

In Ref 13, the electron conduction mechanisms of Section 21-4 are modified to allow for positive hole transfer as well as electron transfer. The modified antibonding molecular orbital mechanism is displayed in Figure 21-2. 

In Fig. 25-4, electron conduction mechanisms are displayed for p and n type semiconductors, which involve silicon doped with gallium and arsenic, respectively. Figure 25-5 gives the following speculative mechanism for electron conduction in the high temperature superconductor YBa2Cu307. It makes use of the instability of Pauling 3-electron bonds under compression (cf. Section 3-10). 

ESR has been employed as a powerful tool in investigations of fundamental electronic conduction mechanisms for ICPs, both in their pristine forms and as blend components [23,59]. Polaronic ICP quasi-particles are responsible for a single resonance line spectra located close to a factor of 2.00. While PE does not present any ESR signal, polyaniline/ PE blends have exhibited symmetrical, single line spectra at about 2.00 attributed to polaronic species (spins) of polyaniline [23,59]. These observations have been used to confirm the presence of the ICP in the polyaniline/ PE blends. 

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